ServiceCollectionScopedBinding.cs

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using System;
using System.Collections.Generic;
using System.Linq;

namespace IoCContainer_net4_sharp5
{
    // The scope is ServiceCollectionScopedBinding (composite it where you see fit: connection, session, thread, etc):
    //   scope1 = new ServiceCollectionScopedBinding(); scope1.Bind<ifoo, foo>(); scope1.Bind<ibar, bar>();
    //   scope2 = new ServiceCollectionScopedBinding(); scope2.Bind<ifoo, foo>(); scope2.Bind<ibar, bar>();
    //   ServiceCollection.Register (scope1);
    //   ServiceCollection.Register (scope2);
    // The scope:instance relation is 1:*.
    // You shall use GetBinding() instead of Get():
    //    ifoo service = ServiceCollection.GetBinding<ifoo> ().Cast<ServiceCollectionScopedBinding> ().Where (scope => scope == myscope).First ().Get<ifoo> ();
    // Its scary but you write it once; also, your scope is whatever you like: even a multi-keyed fractal database for example.
    /// <summary>A set binding that hosts many distinct services per scope (itself).</summary>
    public class ServiceCollectionScopedBinding : ServiceCollectionBinding
    {
        private class DE { public Type type = null; public object instance = null; } // dictionary entry
        private Dictionary<Type, DE> _instances = new Dictionary<Type, DE> ();

        public ServiceCollectionScopedBinding(ServiceCollectionBinding binding = null)
            : base (binding)
        {
            Set = true;
            this.Interface = _instances.Select (kv => kv.Key);
            this.Implementation = _instances.Select (kv => kv.Value.type);
        }

        public override object Create(IInstanceBuilder builder, Type type, object[] args)
        {
            foreach (var kv in _instances)
                if (kv.Value.type == type)
                    return kv.Value.instance ?? (kv.Value.instance = builder.Create (type, args));
            throw new ArgumentException ("Unknown type", "type");
        }

        /// <summary>Bind a service to this binding via its Interface and Implementation.</summary>
        public ServiceCollectionScopedBinding Bind<Interface, Implementation>()
            where Interface : class
            where Implementation : class
        {
            if (_instances.ContainsKey (typeof (Interface)))
                throw new ArgumentException ("Replacing an implementations is off limits.", "Interface");
            _instances[typeof (Interface)] = new DE { type = typeof (Implementation) };
            return this;
        }

        /// <summary>Retrieves a service by its Interface.</summary>
        public Interface Get<Interface>() where Interface : class
        {
            DE result = null;
            if (!_instances.TryGetValue (typeof (Interface), out result))
                throw new ArgumentException ("Type not found.", "Interface");
            if (null == result.instance)
                throw new Exception ("Fixme: service not created.");
            return (Interface)result.instance; // should throw exception when ! (result.instance is Interface)
        }
    }// ServiceCollectionScopedBinding
}