Yet another `Result` types implementation

This library consists of three Result types with some tempting features :

Optional<TValue>
Result<TFault>
Result<TFault, TValue>

Content

License
Installation
- Nuget
- Cement
Examples
Features
Drawbacks
Instantiation of types
Extraction of data from instances
Conversion of generic arguments
- MapValue
- MapFault
- Upcast
Result combining or monadic extensions
Inheritance
Other
Yet to be implemented
Contributing

License

MIT

Installation

Nuget

Execute that command in Package Manager console to install Kontur.Results:

Install-Package Kontur.Results -Version 1.0.1

Execute the following command instead to install Kontur.Results.Monad if you are willing for monadic extensions (implemented separately). It consists of Then, OrElse, Select and do notation:

Install-Package Kontur.Results.Monad -Version 1.0.1

Cement

Use cement to add a reference to Kontur.Results assembly.

Execute that command in your cement module:

cm ref add results your-csproj.csproj

Execute the following command in your cement module instead if you are willing for monadic extensions (implemented separately). It consists of Then, OrElse, Select and do notation:

cm ref add results/monad your-csproj.csproj

Examples

Checking Result status and extracting data with single method

using Kontur.Results;

Result<int, string> result = "success!"; // implicit conversion

if (result.TryGetValue(out string value, out var faultCode))
{
   Console.WriteLine(value.ToString()) // OK. Value is not null here. The compiler allows this.
}

Console.WriteLine("Error code: " + faultCode);
Console.WriteLine(value.ToString()) // warning CS8602: Dereference of a possibly null reference.

Converting Result-way error handling to exception-way error handling

using Kontur.Results;

class DraftError
{
  public int Code { get; init; }
}

class DraftClient
{
   ...
   public Task<Result<DraftError, Draft>> CreateDraft()
   {
     ...
   }
}

Result<DraftError, Draft> createDraftResult = await new DraftClient().CreateDraft();
try
{
  Draft draft = createDraftResult.GetValueOrThrow();
  Console.WriteLine(draft.Id);
}
catch (ResultFailedException<DraftError> ex)
{
  Console.WriteLine("Error code: " + ex.Fault.Code));
}

Working with values without extracting it from Result instances

abstract Task<Optional<string>> GetFormLogin();
abstract Optional<Guid> GetUser(LoginModel login);
abstract ValueTask<Optional<Guid>> CreateUser(LoginModel login);

Task<Optional<Guid>> userId =
   GetFormLogin()
  .MapValue(str => new LoginModel(str))
  .Then(login => GetUser(login).OrElse(() => CreateUser(login)))

Do notation reduces the count of checks and await operators significantly

abstract ValueTask<Result<Exception, Guid>> GetCurrentUserId();
abstract Result<Exception> EnsureUserIdIsCorrect(Guid userId);
abstract Task<int> GetCurrentIndex();
abstract Task<Result<Exception, string>> GetMessage(Guid userId, int index);
abstract Result<Exception, ConvertResult> Convert(string message, Guid userId);

Task<Result<Exception, ConvertResult>> result =
  from userId  in GetCurrentUserId()
  where EnsureUserIdIsCorrect(userId)
  from index   in GetCurrentIndex()
  let nextIndex = index + 1
  from message in GetMessage(userId, nextIndex)
  select Convert(message, userId);

Data parsing

class NaturalNumber
{
  private readonly int value;
  private NaturalNumber(int value) => this.value = value;
  public static NaturalNumber operator +(NaturalNumber a, NaturalNumber b) => new NaturalNumber(a.value + b.value);

  public static bool TryParse(int value, [MaybeNullWhen(returnValue: false)] out NaturalNumber number)
  {
    if (value > 0)
    {
      number = new NaturalNumber(value);
      return true;
    }
    number = null;
    return false;
  }

  public static Optional<NaturalNumber> TryParse(int value) => TryParse(value, out var number) ? number : Optional.None();
  public static NaturalNumber Parse(int value) => TryParse(value).GetValueOrThrow();
}

Result<Exception, int> TryParseString(string input) => int.TryParse(input, out var number)
  ? number
  : new Exception(input + " is not an integer");

Result<Exception, NaturalNumber> result =
  from int1 in TryParseString(Console.ReadLine())
  from natural1 in NaturalNumber.TryParse(int1).OrElse(Result.Fail(new Exception(int1 + " is not positive")))
  from int2 in TryParseString(Console.ReadLine())
  from natural2 in NaturalNumber.TryParse(int2).OrElse(Result.Fail(new Exception(int2 + " is not positive")))
  select natural1 + natural2;

Inheritance to freeze fault type

class StringFaultResult<TValue> : Result<string, TValue>
{
  private readonly Result<string, TValue> result;

  public StringFaultResult(string fault) => result = fault;
  public StringFaultResult(TValue value) => result = value;

  public override TResult Match<TResult>(Func<string, TResult> onFailure, Func<TValue, TResult> onSuccess)
    => result.Match(onFailure, onSuccess);
}

public StringFaultResult<int> GenerateInt()
{
  int randomValue = new Random().Next(0, 10);
  if (randomValue > 0)
  {
    return new StringFaultResult<int>(randomValue);
  }

  return new StringFaultResult<int>("Failed to generate a positive number");
}

Features

Do notation with support of async (Task and ValueTask) execution and without limit on the expression count.
Then (And, ContinueWith, ContinueOnSome, Bind) and OrElse (Or, Else, Catch, ContinueOnNone) async extensions that allow chaining.
Great interface that allows checking and extracting of data with a single method. See TryGetValue and Match.
Explicit behavior of methods. See GetValueOrThrow and GetValueOrDefault. There is no .Result or .Value or .Data properties that have undefined or unexpected behavior if there are no succesful result.
TValue and TFault generic parameters are not restricted in any way.
There is no specific handling of null values. So you can store nulls as TValue or TFault. Use C# 8 nullable reference types to handle nulls.
Assemblies contain only three Result type implementations and extension methods for them. There is no other stuff.
Result<TFault, TValue> has no third state. It is restricted by a schema and the compiler that only two states are possible in memory of an application. One of them is HasValue. Other one is HasFault. So there are no bottom or empty state.
Result type implementations are if-less and make use of abstract classes polymorphism and VMT to maintain simplicity and error safety. As a result, there is no null-forgiving operator and no third state. Also, there are no ternary operators that check Success flag or similar stuff.
Inheritance allows to freeze or limit generic TFault and TValue parameters with user custom type arguments.

Drawbacks

To enable some features the implementation is based on abstract classes polymorphism. So Result types are not marked readonly (but they are implemented as readonly) and are not struct.

Instantiation of types

Explicit examples:

var optional = Optional.Some("hello"); // Optional<string>
var optional = Optional<string>.Some("hello"); // Optional<string>

var result = Result<Exception>.Succeed("hello"); // Result<Exception, string>
var result = Result<Exception, string>.Succeed("hello"); // Result<Exception, string>

var result = Result<Exception>.Succeed(); // Result<Exception>
var result = Result.Succeed<Exception>(); // Result<Exception>

var optional = Optional.None<string>(); // Optional<string>
var optional = Optional<string>.None(); // Optional<string>

var result = ResultFailure<string>.Create(new Exception()); // Result<Exception, string>
var result = Result<Exception, string>.Fail(new Exception()); // Result<Exception, string>

var result = Result.Fail(new Exception()); // Result<Exception>
var result = Result<Exception>.Fail(new Exception()); // Result<Exception>

Implicit examples:

Optional<string> optional = "hello";
Optional<string> optional = Optional.None();

Result<Exception, string> result = "hello";
Result<Exception, string> result = new Exception();
Result<int, int> result = Result.Succeed(55);
Result<int, int> result = Result.Fail(0);

Result<Exception> result = Result.Succeed();
Result<Exception> result = new Exception();

Optional<string> optional = flag
  ? "Hello"
  : Optional.None();

var optional = flag
  ? Optional.Some("Hello")
  : Optional.None();

var optional = flag
  ? "Hello"
  : Optional<string>.None();

Result<Exception, string> result = flag
  ? "hello"
  : new Exception();

var result = flag
  ? "hello"
  : ResultFailure<string>.Create(new Exception());

var result = flag
  ? Result<Exception>.Succeed("hello")
  : new Exception();

Result<int, int> result = flag
  ? Result.Succeed(0)
  : Result.Fail(-1);

var result = flag
  ? Result<int>.Succeed(0)
  : Result.Fail(-1);

var result = flag
  ? Result.Succeed(0)
  : ResultFailure<int>.Create(-1);

Result<Exception> = flag
  ? new Exception()
  : Result.Succeed();

var result = flag
  ? Result<Exception>.Fail(new Exception())
  : Result.Succeed();

var result = flag
  ? new Exception()
  : Result<Exception>.Succeed();

Some conversions:

Result<Exception, int> source = ...

Result<Exception> target = source;

Optional<int> GetResult(Random random)
{
  int randomValue = random.Next(0, 10);
  if (randomValue > 10)
  {
    return randomValue;
  }

  return Optional.None();
}

Extraction of data from instances

TryGetValue

Optional<string> optional = ...;

if (optional.TryGetValue(out string value))
{
  // value is not null here
}

// value may be null here. If you used it, you would get "warning CS8602: Dereference of a possibly null reference"

Result<Exception, string> result = ...;

if (result.TryGetValue(out string value))
{
  // value is not null here
}

// value may be null here. If you used it, you would get "warning CS8602: Dereference of a possibly null reference"

Result<Exception, string> result = ...;

if (result.TryGetValue(out string value, out Exception fault))
{
  // value is not null here
  // fault may be null here. If you used it, you would get "warning CS8602: Dereference of a possibly null reference"
}
else
{
  // fault is not null here
  // value may be null here. If you used it, you would get "warning CS8602: Dereference of a possibly null reference"
}

// Both value and fault may be null here. If you used any of them, you would get "warning CS8602: Dereference of a possibly null reference"

TryGetFault

Result<Exception> result = ...;

if (result.TryGetFault(out Exception fault))
{
  // fault is not null here
}

// fault may be null here. If you used it, you would get "warning CS8602: Dereference of a possibly null reference"

Result<Exception, string> result = ...;

if (result.TryGetFault(out Exception fault))
{
  // fault is not null here
}

// fault may be null here. If you used it, you would get "warning CS8602: Dereference of a possibly null reference"

Result<Exception, string> result = ...;

if (result.TryGetFault(out Exception fault, out string value))
{
  // fault is not null here
  // value may be null here. If you used it, you would get "warning CS8602: Dereference of a possibly null reference"
}
else
{
  // value is not null here
  // fault may be null here. If you use it, you get "warning CS8602: Dereference of a possibly null reference"
}

// Both value and fault may be null here. If you used any of them, you would get "warning CS8602: Dereference of a possibly null reference"

Match

Optional<int> optional = ...;

string extracted = optional.Match(onNone: () => "valueOnNone", onSome: i => $"Number {i}");
string extracted = optional.Match(onNone: () => "valueOnNone", onSome: () => "Number is present");
string extracted = optional.Match(onNone: () => "valueOnNone", onSomeValue: "Number is present");
string extracted = optional.Match(onNoneValue: "valueOnNone", onSome: i => $"Number {i}");
string extracted = optional.Match(onNoneValue: "valueOnNone", onSome: () => "Number is present");
string extracted = optional.Match(onNoneValue: "valueOnNone", onSomeValue: "Number is present");

Examples with upcast

object upcasted = optional.Match(onNone: () => new object(), onSome: i => $"Number {i}");
object upcasted = optional.Match(onNone: () => new object(), onSome: () => "Number is present");
object upcasted = optional.Match(onNone: () => new object(), onSomeValue: "Number is present");
object upcasted = optional.Match(onNoneValue: new object(), onSome: i => $"Number {i}");
object upcasted = optional.Match(onNoneValue: new object(), onSome: () => "Number is present");
object upcasted = optional.Match(onNoneValue: new object(), onSomeValue: "Number is present");

object upcasted = optional.Match(onNone: () => "valueOnNone", onSome: _ => new object());
object upcasted = optional.Match(onNone: () => "valueOnNone", onSome: () => new object());
object upcasted = optional.Match(onNone: () => "valueOnNone", onSomeValue: new object());
object upcasted = optional.Match(onNoneValue: "valueOnNone", onSome: _ => new object());
object upcasted = optional.Match(onNoneValue: "valueOnNone", onSome: () => new object());
object upcasted = optional.Match(onNoneValue: "valueOnNone", onSomeValue: new object());

object upcasted = optional.Match<object>(onNone: () => new Exception("There is no value"), onSome: i => $"Number {i}");
object upcasted = optional.Match<object>(onNone: () => new Exception("There is no value"), onSome: () => "Number is present");
object upcasted = optional.Match<object>(onNone: () => new Exception("There is no value"), onSomeValue: "Number is present");
object upcasted = optional.Match<object>(onNoneValue: new Exception("There is no value"), onSome: i => $"Number {i}");
object upcasted = optional.Match<object>(onNoneValue: new Exception("There is no value"), onSome: () => "Number is present");
object upcasted = optional.Match<object>(onNoneValue: new Exception("There is no value"), onSomeValue: "Number is present");

Result<Exception, int> result = ...;

string extracted = result.Match(onFailure: ex => ex.Message, onSuccess: i => $"Number {i}");
string extracted = result.Match(onFailure: ex => ex.Message, onSuccess: () => "Number is present");
string extracted = result.Match(onFailure: ex => ex.Message, onSuccessValue: "Number is present");
string extracted = result.Match(onFailure: () => "valueOnNone", onSuccess: i => $"Number {i}");
string extracted = result.Match(onFailure: () => "valueOnNone", onSuccess: () => "Number is present");
string extracted = result.Match(onFailure: () => "valueOnNone", onSuccessValue: "Number is present");
string extracted = result.Match(onFailureValue: "valueOnNone", onSuccess: i => $"Number {i}");
string extracted = result.Match(onFailureValue: "valueOnNone", onSuccess: () => "Number is present");
string extracted = result.Match(onFailureValue: "valueOnNone", onSuccessValue: "Number is present");

Examples with upcast

object upcasted = result.Match(onFailure: ex => new object(), onSuccess: i => $"Number {i}");
object upcasted = result.Match(onFailure: ex => new object(), onSuccess: () => "Number is present");
object upcasted = result.Match(onFailure: ex => new object(), onSuccessValue: "Number is present");
object upcasted = result.Match(onFailure: () => new object(), onSuccess: i => $"Number {i}");
object upcasted = result.Match(onFailure: () => new object(), onSuccess: () => "Number is present");
object upcasted = result.Match(onFailure: () => new object(), onSuccessValue: "Number is present");
object upcasted = result.Match(onFailureValue: new object(), onSuccess: i => $"Number {i}");
object upcasted = result.Match(onFailureValue: new object(), onSuccess: () => "Number is present");
object upcasted = result.Match(onFailureValue: new object(), onSuccessValue: "Number is present");

object upcasted = result.Match(onFailure: ex => ex.Message, onSuccess: _ => new object());
object upcasted = result.Match(onFailure: ex => ex.Message, onSuccess: () => new object());
object upcasted = result.Match(onFailure: ex => ex.Message, onSuccessValue: new object());
object upcasted = result.Match(onFailure: () => "valueOnNone", onSuccess: _ => new object());
object upcasted = result.Match(onFailure: () => "valueOnNone", onSuccess: () => new object());
object upcasted = result.Match(onFailure: () => "valueOnNone", onSuccessValue: new object());
object upcasted = result.Match(onFailureValue: "valueOnNone", onSuccess: _ => new object());
object upcasted = result.Match(onFailureValue: "valueOnNone", onSuccess: () => new object());
object upcasted = result.Match(onFailureValue: "valueOnNone", onSuccessValue: new object());

object upcasted = result.Match<object>(onFailure: ex => ex.Message, onSuccess: i => $"Number {i}");
object upcasted = result.Match<object>(onFailure: ex => ex.Message, onSuccess: () => "Number is present");
object upcasted = result.Match<object>(onFailure: ex => ex.Message), onSuccessValue: "Number is present");
object upcasted = result.Match<object>(onFailure: () => new Exception("There is no value"), onSuccess: i => $"Number {i}");
object upcasted = result.Match<object>(onFailure: () => new Exception("There is no value"), onSuccess: () => "Number is present");
object upcasted = result.Match<object>(onFailure: () => new Exception("There is no value"), onSuccessValue: "Number is present");
object upcasted = result.Match<object>(onFailureValue: new Exception("There is no value"), onSuccess: i => $"Number {i}");
object upcasted = result.Match<object>(onFailureValue: new Exception("There is no value"), onSuccess: () => "Number is present");
object upcasted = result.Match<object>(onFailureValue: new Exception("There is no value"), onSuccessValue: "Number is present");

Result<Exception> result = ...;

string extracted = result.Match(onFailure: ex => ex.Message, onSuccess: () => "Fault is not present");
string extracted = result.Match(onFailure: ex => ex.Message, onSuccessValue: "Fault is not present");
string extracted = result.Match(onFailure: () => "valueOnNone", onSuccess: () => "Fault is not present");
string extracted = result.Match(onFailure: () => "valueOnNone", onSuccessValue: "Fault is not present");
string extracted = result.Match(onFailureValue: "valueOnNone", onSuccess: () => "Fault is not present");
string extracted = result.Match(onFailureValue: "valueOnNone", onSuccessValue: "Fault is not present");

Examples with upcast

object upcasted = result.Match(onFailure: ex => new object(), onSuccess: () => "Fault is not present");
object upcasted = result.Match(onFailure: ex => new object(), onSuccessValue: "Fault is not present");
object upcasted = result.Match(onFailure: () => new object(), onSuccess: () => "Fault is not present");
object upcasted = result.Match(onFailure: () => new object(), onSuccessValue: "Fault is not present");
object upcasted = result.Match(onFailureValue: new object(), onSuccess: () => "Fault is not present");
object upcasted = result.Match(onFailureValue: new object(), onSuccessValue: "Fault is not present");

object upcasted = result.Match(onFailure: ex => ex.Message, onSuccess: () => new object());
object upcasted = result.Match(onFailure: ex => ex.Message, onSuccessValue: new object());
object upcasted = result.Match(onFailure: () => "valueOnNone", onSuccess: () => new object());
object upcasted = result.Match(onFailure: () => "valueOnNone", onSuccessValue: new object());
object upcasted = result.Match(onFailureValue: "valueOnNone", onSuccess: () => new object());
object upcasted = result.Match(onFailureValue: "valueOnNone", onSuccessValue: new object());

object upcasted = result.Match<object>(onFailure: ex => ex.Message, onSuccess: () => "Fault is not present");
object upcasted = result.Match<object>(onFailure: ex => ex.Message), onSuccessValue: "Fault is not present");
object upcasted = result.Match<object>(onFailure: () => new Exception(), onSuccess: () => "Fault is not present");
object upcasted = result.Match<object>(onFailure: () => new Exception(), onSuccessValue: "Fault is not present");
object upcasted = result.Match<object>(onFailureValue: new Exception(), onSuccess: () => "Fault is not present");
object upcasted = result.Match<object>(onFailureValue: new Exception(), onSuccessValue: "Fault is not present");

Switch

Optional<int> optional = ...;

optional.Switch(
  onNone: () => Console.WriteLine("There is no value"),
  onSome: value => Console.WriteLine($"Value is {value}")
);

optional.Switch(
  onNone: () => Console.WriteLine("There is no value"),
  onSome: () => Console.WriteLine("Value is present")
);

Result<Exception, int> result = ...;

result.Switch(
  onFailure: fault => Console.WriteLine("Fault is {fault.Message}"),
  onSuccess: value => Console.WriteLine($"Value is {value}")
);

result.Switch(
  onFailure: fault => Console.WriteLine("There is {fault.Message}"),
  onSuccess: () => Console.WriteLine($"Value is present")
);

result.Switch(
  onFailure: () => Console.WriteLine("Fault is present"),
  onSuccess: value => Console.WriteLine($"Value is {value}")
);

result.Switch(
  onFailure: () => Console.WriteLine("Fault is present"),
  onSuccess: () => Console.WriteLine("Value is present")
);

Result<Exception> result = ...;

result.Switch(
  onFailure: fault => Console.WriteLine("Fault is {fault.Message}"),
  onSuccess: () => Console.WriteLine($"There is no fault")
); =

result.Switch(
  onFailure: () => Console.WriteLine("Fault is present"),
  onSuccess: () => Console.WriteLine("There is no fault")
);

OnSome

Optional<int> optional = ...;

optional.OnSome(value => Console.WriteLine($"Value is {value}"));
optional.OnSome(() => Console.WriteLine("Value is present"));

OnNone

Optional<int> optional = ...;

optional.OnNone(() => Console.WriteLine("There is no value"));

OnSuccess

Result<Exception, int> result = ...;

result.OnSuccess(value => Console.WriteLine($"Value is {value}"));
result.OnSuccess(() => Console.WriteLine("Success"));

Result<Exception> result = ...;

result.OnSuccess(() => Console.WriteLine("Success"));

OnFailure

Result<Exception, string> result = ...;

result.OnFailure(fault => Console.WriteLine($"Fault is {fault.Message}"));
result.OnFailure(() => Console.WriteLine("Failure"));

Result<Exception> result = ...;

result.OnFailure(fault => Console.WriteLine($"Fault is {fault.Message}"));
result.OnFailure(() => Console.WriteLine("Failure"));

Switch/OnSome/OnNone/OnSuccess/OnFailure method chaining

Optional<int> optional = ...;

string result = optional
  .Switch(
    onNone: () => Console.WriteLine("There is no value"),
    onSome: value => Console.WriteLine($"Value is {value}"))
  .OnSome(value => Console.WriteLine($"Value is {value}"))
  .OnNone(() => Console.WriteLine("There is no value"))
  .Match(onNoneValue: "valueOnNone", onSome: value => value.ToString());

Result<TFault, TValue> and Result<TFault> have similar syntax.

Switch/OnSome/OnNone/OnSuccess/OnFailure return value upcasting

Optional<string> optional = ...;

Optional<object> upcasted = optional.Switch<object>(
  onNone: () => Console.WriteLine("There is no value"),
  onSome: value => Console.WriteLine($"Value is {value}")
);
Optional<object> upcasted = optional.Switch<object>(
  onNone: () => Console.WriteLine("There is no value"),
  onSome: () => Console.WriteLine("Value is present")
);

Optional<object> upcasted = optional.OnSome<object>(value => Console.WriteLine($"Value is {value}"));
Optional<object> upcasted = optional.OnSome<object>(() => Console.WriteLine("Value is present"));

Optional<object> upcasted = optional.OnNone<object>(() => Console.WriteLine("There is no value"));

Result<TFault, TValue> and Result<TFault> have similar syntax.

GetValueOrElse

Optional<string> optional = ...;

string extracted = optional.GetValueOrElse(() => "defaultValue");
string extracted = optional.GetValueOrElse("defaultValue");

Examples with upcast

object upcasted = optional.GetValueOrElse(() => new object());
object upcasted = optional.GetValueOrElse(new object());

object upcasted = optional.GetValueOrElse<object>(() => new Exception("There is no value"));
object upcasted = optional.GetValueOrElse<object>(new Exception("There is no value"));

Optional<object> objectOptional = ...;
object upcasted = objectOptional.GetValueOrElse(() => "defaultValue");
object upcasted = objectOptional.GetValueOrElse("defaultValue");

Result<Exception, string> result = ...;

string extracted = result.GetValueOrElse(fault => $"Converted to success fault: {fault.Message}");
string extracted = result.GetValueOrElse(() => "defaultValue");
string extracted = result.GetValueOrElse("defaultValue");

Examples with upcast

object upcasted = result.GetValueOrElse(_ => new object());
object upcasted = result.GetValueOrElse(() => new object());
object upcasted = result.GetValueOrElse(new object());

object upcasted = result.GetValueOrElse<object>(fault => new Exception(fault.Message));
object upcasted = result.GetValueOrElse<object>(() => new Exception("There is no value"));
object upcasted = result.GetValueOrElse<object>(new Exception("There is no value"));

Result<Exception, object> objectResult = ...;
object upcasted = objectResult.GetValueOrElse(fault => fault.Message);
object upcasted = objectResult.GetValueOrElse(() => "defaultValue");
object upcasted = objectResult.GetValueOrElse("defaultValue");

GetFaultOrElse

Result<Exception, string> result = ...;

Exception extracted = result.GetFaultOrElse(value => new Exception(value));
Exception extracted = result.GetFaultOrElse(() => new Exception());
Exception extracted = result.GetFaultOrElse(new Exception());

Examples with upcast

object upcasted = result.GetFaultOrElse(_ => new object());
object upcasted = result.GetFaultOrElse(() => new object());
object upcasted = result.GetFaultOrElse(new object());

object upcasted = result.GetFaultOrElse<object>(value => value);
object upcasted = result.GetFaultOrElse<object>(() => "There is no fault");
object upcasted = result.GetFaultOrElse<object>("There is no fault");

Result<object, string> objectResult = ...;
object upcasted = objectResult.GetFaultOrElse(value => value);
object upcasted = objectResult.GetFaultOrElse(() => "defaultFault");
object upcasted = objectResult.GetFaultOrElse("defaultFault");

Result<Exception> result = ...;

Exception extracted = result.GetFaultOrElse(() => new Exception());
Exception extracted = result.GetFaultOrElse(new Exception());

Examples with upcast

object upcasted = result.GetFaultOrElse(() => new object());
object upcasted = result.GetFaultOrElse(new object());

object upcasted = result.GetFaultOrElse<object>(() => "There is no fault");
object upcasted = result.GetFaultOrElse<object>("There is no fault");

Result<object> objectResult = ...;
object upcasted = objectResult.GetFaultOrElse(() => "defaultFault");
object upcasted = objectResult.GetFaultOrElse("defaultFault");

GetValueOrThrow

Optional<string> optional = ...;

string extracted = optional.GetValueOrThrow(); // Throws `ValueMissingException` on None
string extracted = optional.GetValueOrThrow(new Exception("There is no value"));
string extracted = optional.GetValueOrThrow(() => new Exception("There is no value"));

object upcasted = optional.GetValueOrThrow<object>();
object upcasted = optional.GetValueOrThrow<object>(new Exception("There is no value"));
object upcasted = optional.GetValueOrThrow<object>(() => new Exception("There is no value"));

Result<Exception, string> result = ...;

string extracted = result.GetValueOrThrow(); // Throws `ResultFailedException<Exception>` on Failure
string extracted = result.GetValueOrThrow(new Exception("There is no value"));
string extracted = result.GetValueOrThrow(() => new Exception("There is no value"));
string extracted = result.GetValueOrThrow(fault => new Exception(fault.Message));

object upcasted = result.GetValueOrThrow<object>();
object upcasted = result.GetValueOrThrow<object>(new Exception("There is no value"));
object upcasted = result.GetValueOrThrow<object>(() => new Exception("There is no value"));
object upcasted = result.GetValueOrThrow<object>(fault => new Exception(fault.Message));

To override exception thrown by default for a specific TValue you can implement an extension method with the specific TValue in your namespace. You can also use inheritance to override exception thrown by default for TValue in any namespace.

Example

namespace CustomValues
{
  class CustomValue
  {
  }
  static class GetValueOrThrowExtensions
  {
    static CustomValue GetValueOrThrow(this Optional<CustomValue> optional)
    {
      return optional.GetValueOrThrow(new Exception("Overiden!"));
    }

    static CustomValue GetValueOrThrow<TFault>(this Result<TFault, CustomValue> result)
    {
      return result.GetValueOrThrow(new Exception("Overiden!"));
    }
  }
}

GetFaultOrThrow

Result<Exception, string> result = ...;

Exception extracted = result.GetFaultOrThrow(); // Throws `ResultSucceedException<string>` on Success
Exception extracted = result.GetFaultOrThrow(new Exception("There is no fault"));
Exception extracted = result.GetFaultOrThrow(() => new Exception("There is no fault"));
Exception extracted = result.GetFaultOrThrow(value => new Exception(value));

object upcasted = result.GetFaultOrThrow<object>();
object upcasted = result.GetFaultOrThrow<object>(new Exception("There is no fault"));
object upcasted = result.GetFaultOrThrow<object>(() => new Exception("There is no fault"));
object upcasted = result.GetFaultOrThrow<object>(value => new Exception(value));

Result<Exception> result = ...;

Exception extracted = result.GetFaultOrThrow(); // Throws `ResultSucceedException` on Success
Exception extracted = result.GetFaultOrThrow(new Exception("There is no fault"));
Exception extracted = result.GetFaultOrThrow(() => new Exception("There is no fault"));

object upcasted = result.GetFaultOrThrow<object>();
object upcasted = result.GetFaultOrThrow<object>(new Exception("There is no fault"));
object upcasted = result.GetFaultOrThrow<object>(() => new Exception("There is no fault"));

To override exception thrown by default exception for a specific TFault you can implement an extension method with the specific TFault in your namespace. You can also use inheritance to override exception thrown by default for TFault in any namespace.

Example

namespace CustomFaults
{
  class CustomFault
  {
  }
  static class GetValueOrThrowExtensions
  {
    static CustomFault GetFaultOrThrow(this Result<CustomFault> result)
    {
      return result.GetFaultOrThrow(new Exception("Overridden!"));
    }

    static CustomFault GetFaultOrThrow<TValue>(this Result<CustomFault, TValue> result)
    {
      return result.GetFaultOrThrow(new Exception("Overridden!"));
    }
  }
}

GetValueOrDefault

Optional<string> optional = ...;

string? extracted = optional.GetValueOrDefault(); // null or actual value for reference types

object? upcasted = optional.GetValueOrDefault<object>();

Optional<int> optional = ...;

int extracted = optional.GetValueOrDefault();  // 0 or actual value for the value type

Result<Exception, string> result = ...;

string? extracted = result.GetValueOrDefault(); // null or actual value for reference types

object? upcasted = result.GetValueOrDefault<object>();

Result<Exception, int> result = ...;

int extracted = result.GetValueOrDefault();  // 0 or actual value for the value type

GetFaultOrDefault

Result<Exception, string> result = ...;

Exception? extracted = result.GetFaultOrDefault(); // null or actual fault for reference types

object? upcasted = result.GetFaultOrDefault<object>();

Result<int, string> result = ...;

int extracted = result.GetFaultOrDefault();  // 0 or actual fault for the value type

Result<Exception> result = ...;

Exception? extracted = result.GetFaultOrDefault(); // null or actual fault for reference types

object? upcasted = result.GetFaultOrDefault<object>();

Result<int> result = ...;

int extracted = result.GetFaultOrDefault();  // 0 or actual fault for the value type

GetValueOrNull

This method can be applied to non-nullable value types (structs) only.

Optional<int> optional = ...;

int? extracted = optional.GetValueOrNull(); // null or actual value

Result<Exception, int> result = ...;

int? extracted = result.GetValueOrNull(); // null or actual value

Upcasts are not supported.

GetFaultOrNull

This method can be applied to non-nullable value types (structs) only.

Result<int, string> result = ...;

int? extracted = result.GetFaultOrNull(); // null or actual fault

Result<int> result = ...;

int? extracted = result.GetFaultOrNull(); // null or actual fault

Upcasts are not supported.

EnsureHasValue

Optional<string> optional = ...;

// Nothing if `Some`
optional.EnsureHasValue(); // Throws `ValueMissingException` on None
optional.EnsureHasValue(new Exception("There is no value"));
optional.EnsureHasValue(() => new Exception("There is no value"))

To override exception thrown by default exception for a specific TValue you can implement an extension method with the specific TValue in your namespace. You can also use inheritance to override exception thrown by default for TValue in any namespace.

Example

namespace Custom
{
  class CustomValue
  {
  }
  static class EnsureHasValueExtensions
  {
    static void EnsureHasValue(this Optional<CustomValue> optional)
    {
      return optional.EnsureHasValue(new Exception("Overridden!"));
    }
  }
}

EnsureNone

Optional<string> optional = ...;

// Nothing if `None`
optional.EnsureNone(); // Throws `ValueExistsException<string>` if `Some`
optional.EnsureNone(new Exception("There is value"));
optional.EnsureNone(() => new Exception("There is value"))
optional.EnsureNone(value => new Exception($"There is value: {value}"))

To override exception thrown by default exception for a specific TValue you can implement an extension method with the specific TValue in your namespace. You can also use inheritance to override exception thrown by default for TValue in any namespace.

Example

namespace Custom
{
  class CustomValue
  {
  }
  static class EnsureNoneExtensions
  {
    static void EnsureNone(this Optional<CustomValue> optional)
    {
      return optional.EnsureNone(new Exception("Overridden!"));
    }
  }
}

EnsureSuccess

Result<Exception, string> result = ...;

// Nothing if `Success`
result.EnsureSuccess(); // Throws `ResultFailedException<Exception>` on Failure
result.EnsureSuccess(new Exception("There is no value"));
result.EnsureSuccess(() => new Exception("There is no value"))
result.EnsureSuccess(fault => new Exception(fault.Message))

Result<Exception> result = ...;

// Nothing if `Success`
result.EnsureSuccess(); // Throws `ResultFailedException<Exception>` on Failure
result.EnsureSuccess(new Exception("It's failure"));
result.EnsureSuccess(() => new Exception("It's failure"))
result.EnsureSuccess(fault => new Exception(fault.Message))

To override exception thrown by default exception for a specific TValue or TFault you can implement an extension method with the specific TValue or TFault in your namespace. You can also use inheritance to override exception thrown by default for TFault or TValue in any namespace.

Example

namespace CustomTypes
{
  class CustomFault
  {
  }
  class CustomValue
  {
  }
  static class EnsureSuccessExtensions
  {
    static void EnsureSuccess<TFault>(this Result<TFault, CustomValue> result)
    {
      return result.EnsureSuccess(new Exception("Overridden!"));
    }
    static void EnsureSuccess(this Result<CustomFault> result)
    {
      return result.EnsureSuccess(new Exception("Overridden!"));
    }
  }
}

EnsureFailure

Result<Exception, string> result = ...;

// Nothing if `Failure`
result.EnsureFailure(); // Throws `ResultSucceedException<string>` on Success
result.EnsureFailure(new Exception("There is no fault"));
result.EnsureFailure(() => new Exception("There is no fault"))
result.EnsureFailure(value => new Exception(value))

Result<Exception> result = ...;

// Nothing if `Failure`
result.EnsureFailure(); // Throws `ResultSucceedException` on Success
result.EnsureFailure(new Exception("It's success"));
result.EnsureFailure(() => new Exception("It's success"))

To override exception thrown by default exception for a specific TValue or TFault you can implement an extension method with the specific TValue or TFault in your namespace. You can also use inheritance to override exception thrown by default for TFaultor TValue in any namespace.

Example

namespace CustomTypes
{
  class CustomFault
  {
  }
  class CustomValue
  {
  }
  static class EnsureFailureExtensions
  {
    static void EnsureFailure<TFault>(this Result<TFault, CustomValue> result)
    {
      return result.EnsureFailure(new Exception("Overridden!"));
    }
    static void EnsureFailure(this Result<CustomFault> result)
    {
      return result.EnsureFailure(new Exception("Overridden!"));
    }
  }
}

HasSome

Optional<string> optional = "has value";

bool extracted = optional.HasSome; // true

Optional<string> optional = Optional.None();

bool extracted = optional.HasSome; // false

IsNone

Optional<string> optional = "has value";

bool extracted = optional.IsNone; // false

Optional<string> optional = Optional.None();

bool extracted = optional.IsNone; // true

Success

Result<Exception, string> result = "has value";

bool extracted = result.Success; // true

Result<Exception, string> result = new Exception();

bool extracted = result.Success; // false

Result<Exception> result = Result.Succeed();

bool extracted = result.Success; // true

Result<Exception> result = new Exception();

bool extracted = result.Success; // false

Failure

Result<Exception, string> result = "has value";

bool extracted = result.Failure; // false

Result<Exception, string> result = new Exception();

bool extracted = result.Failure; // true

Result<Exception> result = Result.Succeed();

bool extracted = result.Failure; // false

Result<Exception> result = new Exception();

bool extracted = result.Failure; // true

LINQ method syntax (GetValues, GetFaults)

Optional<string> optional = ...;

// `[]` if `None`
// `[value]` if `Some`
IEnumerable<string> values = optional
  .GetValues()
  .ToArray(); // optional

IEnumerable<object> upcasted = optional.GetValues<object>();

Result<Exception, string> result = ...;

// `[]` if `Failure`
// `[value]` if `Success`
IEnumerable<string> values = result.GetValues().ToArray();

IEnumerable<object> upcasted = result.GetValues<object>();

Result<Exception, string> result = ...;

// `[exception]` if `Failure`
// `[]` if `Success`
IEnumerable<Exception> faults = result.GetFaults().ToArray();

IEnumerable<object> upcasted = result.GetFaults<object>();

Result<Exception> result = ...;

// `[exception]` if `Failure`
// `[]` if `Success`
IEnumerable<Exception> faults = result.GetFaults().ToArray();

IEnumerable<object> upcasted = result.GetFaults<object>();

LINQ query syntax

There is no preferred way of combining the IEnumerable and Optional or Result. You can choose a variant that suits your needs and implement it in your project. Some variants are found in the tests folder.

Some examples:

Threat `Result` and `Optional` as containers with single or no elements

This is the simplest variant. But using it results in losing fault details.

Optional

Optional<int> optional = Optional.Some(10);

IEnumerable<int> extracted =
  from value in optional
  from i1 in new [] { 1, 2 }
  from i2 in new [] { 100, 200 }
  select value + i1 + i2;

IEnumerable<int> extracted =
  from i1 in new [] { 1, 2 }
  from value in optional
  from i2 in new [] { 100, 200 }
  select i1 + value + i2;

// extracted is [111, 112, 211, 212].

Optional<int> optional = Optional.Some(10);

IEnumerable<int> extracted =
  from value in optional
  from i1 in new [] { 1, 2 }
  from i2 in Array.Empty<int>()
  select value + i1 + i2;

IEnumerable<int> extracted =
  from i1 in new [] { 1, 2 }
  from value in optional
  from i2 in Array.Empty<int>()
  select i1 + value + i2;

// extracted is empty.

Optional<int> optional = Optional.None();

IEnumerable<int> extracted =
  from value in optional
  from i in new [] { 1, 2 }
  select value + i;

IEnumerable<int> extracted =
  from i in new [] { 1, 2 }
  from value in optional
  select value + i;

// extracted is empty.

To implement it you can use the code

public static IEnumerable<TResult> SelectMany<TValue, TItem, TResult>(
  this IOptional<TValue> optional,
  Func<TValue, IEnumerable<TItem>> collectionSelector,
  Func<TValue, TItem, TResult> resultSelector)
{
  return optional.GetValues().SelectMany(collectionSelector, resultSelector);
}

public static IEnumerable<TResult> SelectMany<TItem, TValue, TResult>(
  this IEnumerable<TItem> collection,
  Func<TItem, IOptional<TValue>> optionSelector,
  Func<TItem, TValue, TResult> resultSelector)
{
  return collection.SelectMany(value => optionSelector(value).GetValues(), resultSelector);
}

Result

Result<Exception, int> result = Result.Succeed(10);

IEnumerable<int> extracted =
  from value in result
  from i1 in new [] { 1, 2 }
  from i2 in new [] { 100, 200 }
  select value + i1 + i2;

IEnumerable<int> extracted =
  from i1 in new [] { 1, 2 }
  from value in result
  from i2 in new [] { 100, 200 }
  select i1 + value + i2;

// extracted is [111, 112, 211, 212].

Result<Exception, int> result = Result.Succeed(10);

IEnumerable<int> extracted =
  from value in result
  from i1 in new [] { 1, 2 }
  from i2 in Array.Empty<int>()
  select value + i1 + i2;

IEnumerable<int> extracted =
  from i1 in new [] { 1, 2 }
  from value in result
  from i2 in Array.Empty<int>()
  select i1 + value + i2;

// extracted is empty.

Result<Exception, int> result = Result.Fail(new Exception());

IEnumerable<int> extracted =
  from value in result
  from i in new [] { 1, 2 }
  select value + i;

IEnumerable<int> extracted =
  from i in new [] { 1, 2 }
  from value in result
  select value + i;

// extracted is empty.

To implement it you can use the code

public static IEnumerable<TResult> SelectMany<TFault, TValue, TItem, TResult>(
  this IResult<TFault, TValue> result,
  Func<TValue, IEnumerable<TItem>> collectionSelector,
  Func<TValue, TItem, TResult> resultSelector)
{
  return result.GetValues().SelectMany(collectionSelector, resultSelector);
}

public static IEnumerable<TResult> SelectMany<TItem, TFault, TValue, TResult>(
  this IEnumerable<TItem> collection,
  Func<TItem, IResult<TFault, TValue>> selector,
  Func<TItem, TValue, TResult> resultSelector)
{
  return collection.SelectMany(value => selector(value).GetValues(), resultSelector);
}

Returning the first found fault

This is is the most useful way of combining data.

Optional

Optional<int> optional = Optional.Some(10);

Optional<IEnumerable<int>> extracted =
  from value in optional
  from i1 in new [] { 1, 2 }
  from i2 in new [] { 100, 200 }
  select value + i1 + i2;

Optional<IEnumerable<int>> extracted =
  from i1 in new [] { 1, 2 }
  from value in optional
  from i2 in new [] { 100, 200 }
  select i1 + value + i2;

// extracted is [111, 112, 211, 212].

Optional<int> optional = Optional.Some(10);

Optional<IEnumerable<int>> extracted =
  from value in optional
  from i1 in new [] { 1, 2 }
  from i2 in Array.Empty<int>()
  select value + i1 + i2;

Optional<IEnumerable<int>> extracted =
  from i1 in new [] { 1, 2 }
  from value in optional
  from i2 in Array.Empty<int>()
  select i1 + value + i2;

// extracted is empty.

Optional<int> optional = Optional.None();

Optional<IEnumerable<int>> extracted =
  from value in optional
  from i in new [] { 1, 2 }
  select value + i;

Optional<IEnumerable<int>> extracted =
  from i in new [] { 1, 2 }
  from value in optional
  select value + i;

// extracted is `None`.

To implement it, four `SelectMany` methods can be used

static Optional<IEnumerable<TResult>> SelectMany<TItem, TValue, TResult>(
  this IEnumerable<TItem> collection,
  Func<TItem, Optional<TValue>> optionalSelector,
  Func<TItem, TValue, TResult> resultSelector)
{
  List<TResult> results = new();
  foreach (var item in collection)
  {
    if (!optionalSelector(item).TryGetValue(out var value))
      return Optional.None();
    results.Add(resultSelector(item, value));
  }
  return results;
}

static Optional<IEnumerable<TResult>> SelectMany<TItem1, TItem2, TResult>(
  this Optional<IEnumerable<TItem1>> optional,
  Func<TItem1, IEnumerable<TItem2>> collectionSelector,
  Func<TItem1, TItem2, TResult> resultSelector) =>
  optional.MapValue(values => values.SelectMany(value => collectionSelector(value).Select(item => resultSelector(value, item))));

static Optional<IEnumerable<TResult>> SelectMany<TValue, TItem, TResult>(
  this Optional<IEnumerable<TValue>> optional,
  Func<TValue, Optional<TItem>> collectionSelector,
  Func<TValue, TItem, TResult> resultSelector) =>
  optional.Match(
    Optional<IEnumerable<TResult>>.None,
    values => SelectMany(values, collectionSelector, resultSelector));

// To allow infinite chaining the following method could be placed in local namespace and other 3 methods can be placed in root namespace
static Optional<IEnumerable<TResult>> SelectMany<TValue, TItem, TResult>(
  this Optional<TValue> optional,
  Func<TValue, IEnumerable<TItem>> collectionSelector,
  Func<TValue, TItem, TResult> resultSelector) =>
  optional.MapValue(value => collectionSelector(value).Select(item => resultSelector(value, item)));

Result

Result<Exception, int> result = Result.Succeed(10);

Result<Exception, IEnumerable<int>> extracted =
  from value in result
  from i1 in new [] { 1, 2 }
  from i2 in new [] { 100, 200 }
  select value + i1 + i2;

Result<Exception, IEnumerable<int>> extracted =
  from i1 in new [] { 1, 2 }
  from value in result
  from i2 in new [] { 100, 200 }
  select i1 + value + i2;

// extracted is [111, 112, 211, 212].

Result<Exception, int> result = Result.Succeed(10);

Result<Exception, IEnumerable<int>> extracted =
  from value in result
  from i1 in new [] { 1, 2 }
  from i2 in Array.Empty<int>()
  select value + i1 + i2;

Result<Exception, IEnumerable<int>> extracted =
  from i1 in new [] { 1, 2 }
  from value in result
  from i2 in Array.Empty<int>()
  select i1 + value + i2;

// extracted is empty.

Result<Exception, int> result = Result.Fail(new Exception("fault"));

Result<Exception, IEnumerable<int>> extracted =
  from value in result
  from i in new [] { 1, 2 }
  select value + i;

Result<Exception, IEnumerable<int>> extracted =
  from i in new [] { 1, 2 }
  from value in result
  select value + i;

// extracted is Exception("fault").

To implement it, four `SelectMany` methods can be used

static Result<TFault, IEnumerable<TResult>> SelectMany<TItem, TFault, TValue, TResult>(
  this IEnumerable<TItem> collection,
  Func<TItem, Result<TFault, TValue>> selector,
  Func<TItem, TValue, TResult> resultSelector)
{
  List<TResult> results = new();
  foreach (var item in collection)
  {
    if (selector(item).TryGetFault(out var fault, out var value))
      return fault;
    results.Add(resultSelector(item, value));
  }
  return results;
}

static Result<TFault, IEnumerable<TResult>> SelectMany<TFault, TItem1, TItem2, TResult>(
  this Result<TFault, IEnumerable<TItem1>> result,
  Func<TItem1, IEnumerable<TItem2>> collectionSelector,
  Func<TItem1, TItem2, TResult> resultSelector) =>
  result.MapValue(values => values.SelectMany(value => collectionSelector(value).Select(item => resultSelector(value, item))));

static Result<TFault, IEnumerable<TResult>> SelectMany<TFault, TValue, TItem, TResult>(
  this Result<TFault, IEnumerable<TValue>> result,
  Func<TValue, Result<TFault, TItem>> collectionSelector,
  Func<TValue, TItem, TResult> resultSelector) =>
  result.Match(
    Result<TFault, IEnumerable<TResult>>.Fail,
    values => SelectMany(values, collectionSelector, resultSelector));

// To allow infinite chaining the following method could be placed in local namespace and other 3 methods can be placed in root namespace
static Result<TFault, IEnumerable<TResult>> SelectMany<TFault, TValue, TItem, TResult>(
            this Result<TFault, TValue> result,
            Func<TValue, IEnumerable<TItem>> collectionSelector,
            Func<TValue, TItem, TResult> resultSelector) =>
            result.MapValue(value => collectionSelector(value).Select(item => resultSelector(value, item)));

foreach

string FindValue(Optional<int> optional)
{
  foreach(var value in optional)
  {
    return value + " is found!";
  }

  return "no value found";
}

string FindValue(Result<Exception, int> result)
{
  foreach(var value in result)
  {
    return value + " is found!";
  }

  return "no value found";
}

ToString

Optional<string> optional = ...;

// `None<string>` if `None`
// `Some<string> value={Value}` if `Some`
string str = optional.ToString();

Result<int, string> result = ...;

// `ResultFailure<Int32, string> fault={Fault}` if `Failure`
// `ResultSuccess<Int32, string> value={Value}` if `Success`
string str = result.ToString();

Result<int> result = ...;

// `ResultFailure<Int32> fault={Fault}` if `Failure`
// `ResultSuccess<Int32>` if `Success`
string str = result.ToString();

Upcasts

You can upcast a return value of many data extraction methods by providing a type argument or by combining two arguments of different types in a single method call.

Examples:

Optional<string> optional = ...

Optional<object> upcasted1 = optional.OnNone<object>(str => Console.WriteLine(str));
Optional<object> upcasted2 = optional.Match(onNone: () => new object(), onSome: str => str);

Only safe upcasts are allowed. For example, Optional<string> can be converted to Optional<object> but not vice versa.

Safety is enforced by covariance rules. So:

Upcasts are only supported for reference types because covariance can not be used with value types.
Upcasts are only supported for synchronous methods because Task<T> and ValueTask<T> types do not support covariance.

Conversion of generic arguments

All conversion methods except Upcast method support async extensions for every listed synchronous scenario. All synchronous methods support upcasts of TFault and TValue.

Async extensions make use of methods returning Task<T>, ValueTask<T> and inline async lambdas. For example:

async Task<int> Get1(int number) => number + 1;
async ValueTask<int> Get2(number) => number - 1;

Task<Optional<int>> Get(Task<Optional<int>> optional)
{
  return optional
    .MapValue(i => Get1(i))
    .MapValue(i => Get2(i))
    .MapValue(async i => await Get1(i));
}

If there is at least one async method in a chain returning Task<T> the result is Task<T2>. Otherwise, the result is ValueTask<T2>.

MapValue

MapValue changes value or/and type of TValue.

Optional<string> optional = ...;

Optional<string> extracted = optional.MapValue(str => str + "suffix");
Optional<string> extracted = optional.MapValue(() => "new value");
Optional<string> extracted = optional.MapValue("other string");

Optional<int> extracted = optional.MapValue(str => int.Parse(str));
Optional<int> extracted = optional.MapValue(() => int.Parse("123"));
Optional<int> extracted = optional.MapValue(15);

Async examples

Optional<string> optional = ...;

ValueTask<Optional<string>> extracted = optional.MapValue(async str => await Task.FromResult(str));
ValueTask<Optional<string>> extracted = optional.MapValue(str => new ValueTask(str));
Task<Optional<string>> extracted = optional.MapValue(str => Task.FromResult(str));

ValueTask<Optional<string>> optional = ...;

ValueTask<Optional<string>> extracted = optional.MapValue(str => str + "suffix");
ValueTask<Optional<string>> extracted = optional.MapValue(async str => await Task.FromResult(str));
ValueTask<Optional<string>> extracted = optional.MapValue(str => new ValueTask(str));
Task<Optional<string>> extracted = optional.MapValue(str => Task.FromResult(str));

Task<Optional<string>> optional = ...;

Task<Optional<string>> extracted = optional.MapValue(str => str + "suffix");
Task<Optional<string>> extracted = optional.MapValue(async str => await Task.FromResult(str));
Task<Optional<string>> extracted = optional.MapValue(str => new ValueTask(str));
Task<Optional<string>> extracted = optional.MapValue(str => Task.FromResult(str));

Result<Guid, string> result = ...;

Result<Guid, string> extracted = result.MapValue(str => str + "suffix");
Result<Guid, string> extracted = result.MapValue(() => "new value");
Result<Guid, string> extracted = result.MapValue("other string");

Result<Guid, int> extracted = result.MapValue(str => int.Parse(str));
Result<Guid, int> extracted = result.MapValue(() => int.Parse("123"));
Result<Guid, int> extracted = result.MapValue(15);

Async examples

Result<Guid, string> result = ...;

ValueTask<Result<Guid, string>> extracted = result.MapValue(async str => await Task.FromResult(str));
ValueTask<Result<Guid, string>> extracted = result.MapValue(str => new ValueTask(str));
Task<Result<Guid, string>> extracted = result.MapValue(str => Task.FromResult(str));

ValueTask<Result<Guid, string>> result = ...;

ValueTask<Result<Guid, string>> extracted = result.MapValue(str => str + "suffix");
ValueTask<Result<Guid, string>> extracted = result.MapValue(async str => await Task.FromResult(str));
ValueTask<Result<Guid, string>> extracted = result.MapValue(str => new ValueTask(str));
Task<Result<Guid, string>> extracted = result.MapValue(str => Task.FromResult(str));

Task<Result<Guid, string>> result = ...;

Task<Result<Guid, string>> extracted = result.MapValue(str => str + "suffix");
Task<Result<Guid, string>> extracted = result.MapValue(async str => await Task.FromResult(str));
Task<Result<Guid, string>> extracted = result.MapValue(str => new ValueTask(str));
Task<Result<Guid, string>> extracted = result.MapValue(str => Task.FromResult(str));

MapFault

MapFault changes value or/and type of TFault.

Result<string, Guid> result = ...;

Result<string, Guid> extracted = result.MapFault(str => str + "suffix");
Result<string, Guid> extracted = result.MapFault(() => "new fault");
Result<string, Guid> extracted = result.MapFault("other string");

Result<int, Guid> extracted = result.MapFault(str => int.Parse(str));
Result<int, Guid> extracted = result.MapFault(() => int.Parse("123"));
Result<int, Guid> extracted = result.MapFault(15);

Async examples

Result<string, Guid> result = ...;

ValueTask<Result<string, Guid>> extracted = result.MapFault(async str => await Task.FromResult(str));
ValueTask<Result<string, Guid>> extracted = result.MapFault(str => new ValueTask(str));
Task<Result<string, Guid>> extracted = result.MapFault(str => Task.FromResult(str));

ValueTask<Result<string, Guid>> result = ...;

ValueTask<Result<string, Guid>> extracted = result.MapFault(str => str + "suffix");
ValueTask<Result<string, Guid>> extracted = result.MapFault(async str => await Task.FromResult(str));
ValueTask<Result<string, Guid>> extracted = result.MapFault(str => new ValueTask(str));
Task<Result<string, Guid>> extracted = result.MapFault(str => Task.FromResult(str));

Task<Result<string, Guid>> result = ...;

Task<Result<string, Guid>> extracted = result.MapFault(str => str + "suffix");
Task<Result<string, Guid>> extracted = result.MapFault(async str => await Task.FromResult(str));
Task<Result<string, Guid>> extracted = result.MapFault(str => new ValueTask(str));
Task<Result<string, Guid>> extracted = result.MapFault(str => Task.FromResult(str));

Result<string> result = ...;

Result<string> extracted = result.MapFault(str => str + "suffix");
Result<string> extracted = result.MapFault(() => "new fault");
Result<string> extracted = result.MapFault("other string");

Result<int> extracted = result.MapFault(str => int.Parse(str));
Result<int> extracted = result.MapFault(() => int.Parse("123"));
Result<int> extracted = result.MapFault(15);

Async examples

Result<string> result = ...;

ValueTask<Result<string>> extracted = result.MapFault(async str => await Task.FromResult(str));
ValueTask<Result<string>> extracted = result.MapFault(str => new ValueTask(str));
Task<Result<string>> extracted = result.MapFault(str => Task.FromResult(str));

ValueTask<Result<string>> result = ...;

ValueTask<Result<string>> extracted = result.MapFault(str => str + "suffix");
ValueTask<Result<string>> extracted = result.MapFault(async str => await Task.FromResult(str));
ValueTask<Result<string>> extracted = result.MapFault(str => new ValueTask(str));
Task<Result<string>> extracted = result.MapFault(str => Task.FromResult(str));

Task<Result<string>> result = ...;

Task<Result<string>> extracted = result.MapFault(str => str + "suffix");
Task<Result<string>> extracted = result.MapFault(async str => await Task.FromResult(str));
Task<Result<string>> extracted = result.MapFault(str => new ValueTask(str));
Task<Result<string>> extracted = result.MapFault(str => Task.FromResult(str));

Upcast

Optional<string> optional = ...;

// Compiles
Optional<object> objectOptional = optional.Upcast<object>();

// Does not compile
var doesNotCompile = objectOptional.Upcast<string>();

Result<string> result = ...;

// Compiles
Result<object> objectResult = result.Upcast<object>();

// Does not compile
var doesNotCompile = objectResult.Upcast<string>();

Result<string, string> result = ...;

// Compiles
Result<object, string> objectResult1 = result.Upcast<object, string>();
Result<string, object> objectResult2 = result.Upcast<string, string>();
Result<object, object> objectResult3 = result.Upcast<object, object>();

// Does not compile
var doesNotCompile = objectResult1.Upcast<string, string>();
var doesNotCompile = objectResult2.Upcast<string, string>();
var doesNotCompile = objectResult3.Upcast<string, string>();

Async extensions are not supported Upcast methods.

Result combining

There are some monadic extensions that can help you to reduce lines and errors in your code. All Optional/Result combining methods support async extensions for every listed synchronous scenario.

Currently synchronous Optional/Result combining methods do not support upcasts of TFault and TValue.

Then

Then is Then (And, ContinueWith, ContinueOnSome, Bind) Result combining method.

If a first optional/result is None/Failure then the None/Failure is returned. If the first optional/result is Some/Success then a second optional/result is returned. The second Optional/Result factory method is only executed if the first Optional/Result is Some/Success.

TFault types should be identical. Upcasts are not supported yet. TValue types can be different.

Optional<int> optional1 = ...;
Optional<string> optional2 = ...;

// If optional1 is None then None is returned.
// Otherwise optional2 is returned.
Optional<string> result = optional1.Then(optional2);
Optional<string> result = optional1.Then(() => optional2);
Optional<string> result = optional1.Then(i => i > 10 ? Optional<string>.Some(i.ToString()) : Optional<string>.None());

Async examples

Optional<int> optional1 = ...;
Optional<string> optional2 = ...;

ValueTask<Optional<string>> result = optional1.Then(async value => await Task.FromResult(optional2));
ValueTask<Optional<string>> result = optional1.Then(value => new ValueTask(optional2));
Task<Optional<string>> result = optional1.Then(value => Task.FromResult(optional2));

ValueTask<Optional<string>> result = new ValueTask(optional1).Then(value => optional2);
ValueTask<Optional<string>> result = new ValueTask(optional1).Then(async value => await Task.FromResult(optional2));
ValueTask<Optional<string>> result = new ValueTask(optional1).Then(value => new ValueTask(optional2));
Task<Optional<string>> result = new ValueTask(optional1).Then(value => Task.FromResult(optional2));

Task<Optional<string>> result = Task.FromResult(optional1).Then(value => optional2);
Task<Optional<string>> result = Task.FromResult(optional1).Then(async value => await Task.FromResult(optional2));
Task<Optional<string>> result = Task.FromResult(optional1).Then(value => new ValueTask(optional2));
Task<Optional<string>> result = Task.FromResult(optional1).Then(value => Task.FromResult(optional2));

Result<Exception, int> result1 = ...;
Result<Exception, string> result2 = ...;

// If option1 is None then None is returned.
// Otherwise option2 is returned.
Result<Exception, string> result = result1.Then(result2);
Result<Exception, string> result = result1.Then(() => result2);
Result<Exception, string> result = result1.Then(i => i > 10 ? Result<Exception, string>.Success(i.ToString()) : Result<Exception, string>.Failure());

Async examples

Result<Exception, int> result1 = ...;
Result<Exception, string> result2 = ...;

ValueTask<Result<Exception, string>> result = result1.Then(async value => await Task.FromResult(result2));
ValueTask<Result<Exception, string>> result = result1.Then(value => new ValueTask(result2));
Task<Result<Exception, string>> result = result1.Then(value => Task.FromResult(result2));

ValueTask<Result<Exception, string>> result = new ValueTask(result1).Then(value => result2);
ValueTask<Result<Exception, string>> result = new ValueTask(result1).Then(async value => await Task.FromResult(result2));
ValueTask<Result<Exception, string>> result = new ValueTask(result1).Then(value => new ValueTask(result2));
Task<Result<Exception, string>> result = new ValueTask(result1).Then(value => Task.FromResult(result2));

Task<Result<Exception, string>> result = Task.FromResult(result1).Then(value => result2);
Task<Result<Exception, string>> result = Task.FromResult(result1).Then(async value => await Task.FromResult(result2));
Task<Result<Exception, string>> result = Task.FromResult(result1).Then(value => new ValueTask(result2));
Task<Result<Exception, string>> result = Task.FromResult(result1).Then(value => Task.FromResult(result2));

All meaningful combinations of Optional<TValue>, Result<TFault> and Result<TFault, TValue> are also supported.

OrElse

OrElse is Or (OrElse, Else, Catch, ContinueOnNone) Result combining method.

If a first optional/result is Some/Success then it is returned. If the first optional/result is None/Failure then a second optional/result is returned. The second Optional/Result factory method is only executed if the first Optional/Result is None/Failure.

TValue types should be identical. Upcasts are not supported yet. TFault types can be different.

Optional<string> optional1 = ...;
Optional<string> optional2 = ...;

// If optional1 is Some then option1 is returned.
// Otherwise optional2 is returned.
Optional<string> result = optional1.OrElse(optional2);
Optional<string> result = optional1.OrElse(() => optional2);

Async examples

Optional<string> optional1 = ...;
Optional<string> optional2 = ...;

ValueTask<Optional<string>> result = optional1.OrElse(async () => await Task.FromResult(optional2));
ValueTask<Optional<string>> result = optional1.OrElse(() => new ValueTask(optional2));
Task<Optional<string>> result = optional1.OrElse(() => Task.FromResult(optional2));

ValueTask<Optional<string>> result = new ValueTask(optional1).OrElse(() => optional2);
ValueTask<Optional<string>> result = new ValueTask(optional1).OrElse(async () => await Task.FromResult(optional2));
ValueTask<Optional<string>> result = new ValueTask(optional1).OrElse(() => new ValueTask(optional2));
Task<Optional<string>> result = new ValueTask(optional1).OrElse(() => Task.FromResult(optional2));

Task<Optional<string>> result = Task.FromResult(optional1).OrElse(() => optional2);
Task<Optional<string>> result = Task.FromResult(optional1).OrElse(async () => await Task.FromResult(optional2));
Task<Optional<string>> result = Task.FromResult(optional1).OrElse(() => new ValueTask(optional2));
Task<Optional<string>> result = Task.FromResult(optional1).OrElse(() => Task.FromResult(optional2));

Result<int, string> result1 = ...;
Result<Exception, string> result2 = ...;

// If option1 is Some then option1 is returned.
// Otherwise option2 is returned.
Result<Exception, string> result = result1.OrElse(result2);
Result<Exception, string> result = result1.OrElse(() => result2);
Result<Exception, string> result = result1.OrElse(fault => result2);

Async examples

Result<int, string> result1 = ...;
Result<Exception, string> result2 = ...;

ValueTask<Result<Exception, string>> result = result1.OrElse(async fault => await Task.FromResult(result2));
ValueTask<Result<Exception, string>> result = result1.OrElse(fault => new ValueTask(result2));
Task<Result<Exception, string>> result = result1.OrElse(fault => Task.FromResult(result2));

ValueTask<Result<sException, tring>> result = new ValueTask(result1).OrElse(fault => result2);
ValueTask<Result<sException, tring>> result = new ValueTask(result1).OrElse(async fault => await Task.FromResult(result2));
ValueTask<Result<Exception, string>> result = new ValueTask(result1).OrElse(fault => new ValueTask(result2));
Task<Result<Exception, string>> result = new ValueTask(result1).OrElse(fault => Task.FromResult(result2));

Task<Result<Exception, string>> result = Task.FromResult(result1).OrElse(fault => result2);
Task<Result<Exception, string>> result = Task.FromResult(result1).OrElse(async fault => await Task.FromResult(result2));
Task<Result<Exception, string>> result = Task.FromResult(result1).OrElse(fault => new ValueTask(result2));
Task<Result<Exception, string>> result = Task.FromResult(result1).OrElse(fault => Task.FromResult(result2));

All meaningful combinations of Optional<TValue>, Result<TFault> and Result<TFault, TValue> are also supported.

Then/OrElse method chaining

abstract Optional<string> GetFormLogin();
abstract Optional<Guid> GetUser(string login);
abstract Task<Optional<Guid>> CreateUser(string login);
abstract Optional<DateTime> GetCreationDate(Guid userId);

Task<Optional<long>> userCreationDateTicks =
   GetFormLogin()
  .Then(login => GetUser(login).OrElse(() => CreateUser(login)))
  .Then(userId => GetCreationDate(userId))
  .MapValue(date => date.Ticks);

abstract Result<TicksError, string> GetFormLogin();
abstract Result<UserException, Guid> GetUser(string login);
abstract Task<Result<TicksError, Guid>> CreateUser(string login);
abstract Result<TicksError, DateTime> GetCreationDate(Guid userId);
abstract Result<TicksError> EnsureTicksIsValid(long ticks);

Task<Result<GetTicksError>> userCreationDateTicksValid =
   GetFormLogin()
  .Then(login => GetUser(login).OrElse(() => CreateUser(login)))
  .Then(userId => GetCreationDate(userId))
  .MapValue(date => date.Ticks);
  .Then(ticks => EnsureTicksIsValid(ticks))

Select

Select is a mix of MapValue and Then. Like both of them, a factory method of a second Optional/Result or value is only executed if the first Optional/Result is Some/Success. Like MapValue it allows changing type and value by using value factory. Unlike MapValue and like Then it allows creating a second Optional/Result which is a result of the whole operation. It also allows you to change Some/Success to None/Failure if you want.

TFault types should be identical. Upcasts are not supported yet. TValue types can be different.

Optional examples

Optional<string> optional = ...;

Optional<string> extracted = optional.Select(str => str.Length > 5 ? Optional.Some(str) : Optional.None());
Optional<string> extracted = optional.Select(str => str + "suffix");
Optional<int> extracted = optional.Select(str => int.Parse(str));

ValueTask<Optional<int>> extracted = optional.Select(async str => await Task.FromResult(int.Parse(str)));
ValueTask<Optional<int>> extracted = optional.Select(str => new ValueTask(int.Parse(str)));
Task<Optional<int>> extracted = optional.Select(str => Task.FromResult(int.Parse(str)));

ValueTask<Optional<int>> extracted = new ValueTask(optional).Select(async str => await Task.FromResult(int.Parse(str)));
ValueTask<Optional<int>> extracted = new ValueTask(optional).Select(str => new ValueTask(int.Parse(str)));
Task<Optional<int>> extracted = new ValueTask(optional).Select(str => Task.FromResult(int.Parse(str)));

Task<Optional<int>> extracted = Task.FromResult(optional).Select(async str => await Task.FromResult(int.Parse(str)));
Task<Optional<int>> extracted = Task.FromResult(optional).Select(str => new ValueTask(int.Parse(str)));
Task<Optional<int>> extracted = Task.FromResult(optional).Select(str => Task.FromResult(int.Parse(str)));

Result examples

Result<Exception, string> result = ...;

Result<Exception, string> extracted = result.Select(str => str.Length > 5 ? Result<Exception, string>.Succeed(str) : Result<Exception, string>.Fail(new Exception(str)));
Result<Exception, string> extracted = result.Select(str => str + "suffix");
Result<Exception, int> extracted = result.Select(str => int.Parse(str));

ValueTask<Optional<int>> extracted = result.Select(async str => await Task.FromResult(int.Parse(str)));
ValueTask<Optional<int>> extracted = result.Select(str => new ValueTask(int.Parse(str)));
Task<Optional<int>> extracted = result.Select(str => Task.FromResult(int.Parse(str)));

ValueTask<Optional<int>> extracted = new ValueTask(result).Select(str => int.Parse(str));
ValueTask<Optional<int>> extracted = new ValueTask(result).Select(async str => await Task.FromResult(int.Parse(str)));
ValueTask<Optional<int>> extracted = new ValueTask(result).Select(str => new ValueTask(int.Parse(str)));
Task<Optional<int>> extracted = new ValueTask(result).Select(str => Task.FromResult(int.Parse(str)));

Task<Optional<int>> extracted = Task.FromResult(result).Select(str => int.Parse(str));
Task<Optional<int>> extracted = Task.FromResult(result).Select(async str => await Task.FromResult(int.Parse(str)));
Task<Optional<int>> extracted = Task.FromResult(result).Select(str => new ValueTask(int.Parse(str)));
Task<Optional<int>> extracted = Task.FromResult(result).Select(str => Task.FromResult(int.Parse(str)));

Do notation

abstract Optional<Guid> GetCurrentUserId();
abstract Optional<int> GetCurrentIndex();
abstract Optional<Product> GetCurrentProduct();
abstract Optional<string> GetMessage(Guid userId, int index, Product product);
abstract Optional<ConvertResult> Convert(string message, Product product);

Optional<ConvertResult> result =
  from userId  in GetCurrentUserId()
  where userId != Guid.Empty
  from index   in GetCurrentIndex()
  from product in GetCurrentProduct()
  let nextIndex = index + 1
  from message in GetMessage(userId, nextIndex, product)
  select Convert(message, product);

The last select expression can return either Optional<TResult> or just TResult.

abstract Result<Exception, Guid> GetCurrentUserId();
abstract Result<Exception> EnsureUserIdIsCorrect(Guid userId);
abstract Result<Exception, int> GetCurrentIndex();
abstract Result<Exception, Product> GetCurrentProduct();
abstract Result<int, string> GetMessage(Guid userId, int index, Product product);
abstract Result<Exception, ConvertResult> Convert(string message, Product product);

Result<Exception, ConvertResult> result =
  from userId  in GetCurrentUserId()
  where EnsureUserIdIsCorrect(userId)
  from index   in GetCurrentIndex()
  from product in GetCurrentProduct()
  let nextIndex = index + 1
  from message in GetMessage(userId, nextIndex, product).MapFault(i => new Exception(i.ToString()))
  select Convert(message, product);

The last select expression can return Result<Exception, TResult>, Result<Exception> or just TResult. TFault should be identical in all clauses. Use MapFault to convert different TFault to the same one.

Do notation with async extensions

abstract Optional<Guid> GetCurrentUserId();
abstract Task<int> GetCurrentIndex();
abstract ValueTask<Optional<Product>> GetCurrentProduct();
abstract Task<Optional<string>> GetMessage(Guid userId, int index, Product product);
abstract Task<Format> GetFormat(int index, string message);
abstract Optional<ConvertResult> Convert(string message, Format format);
abstract Task<bool> IsValid(int index);

Task<Optional<ConvertResult>> result =
  from userId  in GetCurrentUserId() // A
  where userId != Guid.Empty       // B
  from index   in GetCurrentIndex() // C
  from product in GetCurrentProduct() // D
  let nextIndex = index + 1
  where IsValid(nextIndex) // E
  from message in GetMessage(userId, nextIndex, product) // F
  from format  in GetFormat(nextIndex, message) // G
  select Convert(message, format); // H

Where:

A (first from/in clause) must return Optional<T>, ValueTask<Optional<T>> or Task<Optional<T>>.
B and E (where clause) may return bool, ValueTask<bool> or Task<bool>.
C, D, F and G (subsequent from/in clause) may return one of Optional<T>, ValueTask<T>, ValueTask<Optional<T>>, Task<T> or Task<Optional<T>>. Subsequent expressions may depend on previous expressions (F and G for example) or may not depend on previous expressions (C and D for example). The total count of B, C, D, E, F and G-like statements is efficiently unlimited.
H (select clause) should return TResult, Optional<TResult>, ValueTask<TResult>, ValueTask<Optional<TResult>>, Task<TResult> or Task<Optional<TResult>>.

abstract Result<Exception, Guid> GetCurrentUserId();
abstract Result<Exception> EnsureUserIdIsCorrect(Guid userId);
abstract Task<int> GetCurrentIndex();
abstract ValueTask<Result<Exception, Product>> GetCurrentProduct();
abstract Task<Result<int, string>> GetMessage(Guid userId, int index, Product product);
abstract Task<Format> GetFormat(int index, string message);
abstract Result<Exception, ConvertResult> Convert(string message, Format format);
abstract Task<Result<Exception>> IsValid(int index);

Task<Result<Exception, ConvertResult>> result =
  from userId  in GetCurrentUserId() // A
  where EnsureUserIdIsCorrect(userId) // B
  from index   in GetCurrentIndex() // C
  from product in GetCurrentProduct() // D
  let nextIndex = index + 1
  where IsValid(nextIndex) // E
  from message in GetMessage(userId, nextIndex, product).MapFault(i => new Exception(i.ToString())) // F
  from format  in GetFormat(nextIndex, message) // G
  select Convert(message, format); // H

Where:

A (first from/in clause) must return Result<TFault, TValue>, ValueTask<Result<TFault, TValue>> or Task<Result<TFault, TValue>>.
B and E (where clause) may return Result<TFault>, ValueTask<Result<TFault>> or Task<Result<TFault>>.
C, D, F and G (subsequent from/in clause) may return one of Result<TFault, TValue>, ValueTask<TValue>, ValueTask<Result<TFault, TValue>>, Task<TValue> or Task<Result<TFault, TValue>>. Subsequent expressions may depend on previous expressions (F and G for example) or may not depend on previous expressions (C and D for example). The total count of B, C, D, E, F and G-like statements is efficiently unlimited.
H (select clause) should return TResult, Result<TFault>, Result<TFault, TResult>, ValueTask<TResult>, ValueTask<Result<TFault>>, ValueTask<Result<TFault, TResult>>, Task<TResult>, Task<Result<TFault>> or Task<Result<TFault, TResult>>.

TFault should be identical in all clauses. Use MapFault to convert different TFault to the same one.

Inheritance

You can create your own Result type by inheriting provided types.

class StringFaultResult<TValue> : Result<string, TValue>
{
  private readonly Result<string, TValue> result;

  public StringFaultResult(string fault) => result = Fail(fault);

  public StringFaultResult(TValue value) => result = Succeed(value);

  public override TResult Match<TResult>(Func<string, TResult> onFailure, Func<TValue, TResult> onSuccess)
    => result.Match(onFailure, onSuccess);
}

All synchronous methods are inherited.

If you inherit, to bring back some lost features you can reimplement the following:

implicit conversion operators
some async extensions that do not inherit by default due to invariance of Task<T> and ValueTask<T>

Because this implementation relies heavily on C# 9 source generators it is not a hard task to implement a new feature that reimplements lost features automatically. Send me requests if you need such a feature.

You can also override extensions methods. For example:

MapValue to override return type with inherited type
GetValueOrThrow to override Exception type thrown by default

Other

Equals and GetHashCode make use of type arguments, faults and values (if present) for calculations.
There is no fold method.

Yet to be implemented

(easy) Currently only Result combining methods (Map, Select, Then, OrElse and do notation), MapValue and MapFault support async extensions with Task or ValueTask types. Data extraction methods (like TryGetValue, Switch or GetOrThrow) only support synchronous execution.
(easy) Currently monadic extensions (Select, Then, OrElse and do notation) do not support upcasts for synchronous methods.
(medium) Implement do-notations (LINQ Query Syntax) for collections.
(medium) Currently implemented source generators can not generate async extensions and implicit conversion operators for custom inherited classes in your assemblies.
(hard) Do notation for Result<TFault, TValue> with different TFault type arguments is possible in a limited way but unimplemented. If it is implemented, it would disallow a few struct type arguments for TFault and would not enable all scenarios of selecting Result<TFaultOther> with different TFault argument in subsequent from/in clauses. The current workaround is to use MapFault method before passing Result to a do notation clause.

Send me your requests if you need such features.

Contributing

Contributions are appreciated.

Name		Name	Last commit message	Last commit date
Latest commit History 66 Commits
Kontur.Results.Monad		Kontur.Results.Monad
Kontur.Results.SourceGenerator.Monad		Kontur.Results.SourceGenerator.Monad
Kontur.Results.SourceGenerator.Shared		Kontur.Results.SourceGenerator.Shared
Kontur.Results.SourceGenerator		Kontur.Results.SourceGenerator
Kontur.Results		Kontur.Results
Kontur.Tests.Results		Kontur.Tests.Results
vostok.devtools		vostok.devtools
.build_nuget.bat		.build_nuget.bat
.editorconfig		.editorconfig
.gitignore		.gitignore
Directory.Build.props		Directory.Build.props
Kontur.Results.DotSettings		Kontur.Results.DotSettings
Kontur.Results.sln		Kontur.Results.sln
LICENSE		LICENSE
README.md		README.md

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Yet another Result types implementation

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Instantiation of types

Extraction of data from instances

TryGetValue

TryGetFault

Match

Switch

OnSome

OnNone

OnSuccess

OnFailure

Switch/OnSome/OnNone/OnSuccess/OnFailure method chaining

Switch/OnSome/OnNone/OnSuccess/OnFailure return value upcasting

GetValueOrElse

GetFaultOrElse

GetValueOrThrow

GetFaultOrThrow

GetValueOrDefault

GetFaultOrDefault

GetValueOrNull

GetFaultOrNull

EnsureHasValue

EnsureNone

EnsureSuccess

EnsureFailure

HasSome

IsNone

Success

Failure

LINQ method syntax (GetValues, GetFaults)

LINQ query syntax

Threat Result and Optional as containers with single or no elements

Optional

Result

Returning the first found fault

Optional

Result

foreach

ToString

Upcasts

Conversion of generic arguments

MapValue

MapFault

Upcast

Result combining

Then

OrElse

Then/OrElse method chaining

Select

Do notation

Do notation with async extensions

Inheritance

Other

Yet to be implemented

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Yet another `Result` types implementation

Threat `Result` and `Optional` as containers with single or no elements

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