feat: Create Singleton func for convenient singleton construction #1297
Conversation
github-actions
bot
changed the title
go-runtime/ftl/singleton.go
Outdated
|
|
||
| type InputLambda[T any] func(context.Context) (T, error) | ||
|
|
||
| type SingletonConstructor[T any] struct { |
There was a problem hiding this comment.
Call this SingletonHandle
go-runtime/ftl/singleton.go
Outdated
| "sync" | ||
| ) | ||
|
|
||
| type InputLambda[T any] func(context.Context) (T, error) |
There was a problem hiding this comment.
Let's not worry about the intermediate type - the signature is so simple that I think it just adds noise rather than reducing it.
There was a problem hiding this comment.
Sounds good, removed
go-runtime/ftl/singleton.go
Outdated
| type SingletonConstructor[T any] struct { | ||
| Fn InputLambda[T] | ||
| Out T | ||
| Once sync.Once |
There was a problem hiding this comment.
These should be private (lowercase).
There was a problem hiding this comment.
BTW with the Go LSP there's usually a "Rename symbol" option which will correctly rename the symbol everywhere it's used.
| var sf SingletonConstructor[T] | ||
| sf.Fn = fn | ||
| return sf | ||
| } |
There was a problem hiding this comment.
To solve this you'll need to make once sync.Once into a pointer -once *sync.Once and construct it when you're creating the handle:
return SingletonConstructor[T]{fn: fn, once: &sync.Once{}}There was a problem hiding this comment.
Ahhhh that's a much nicer way of doing it - thanks!
go-runtime/ftl/singleton_test.go
Outdated
| ctx := context.Background() | ||
| once := Singleton[string](func(ctx context.Context) (string, error) { | ||
| panic("test panic") | ||
| return "only once", nil |
There was a problem hiding this comment.
This should return an error to invoke the panic in the singleton?
There was a problem hiding this comment.
Whoops, thanks for catching that!
Co-authored-by: Alec Thomas <[email protected]>
Fixes issue #1295