Add support for async factory methods

[jpierson]

We use the Ninject factory extensions in a project that I'm working on and we have come across the need in some cases for async instantiation which has come into conflict with some of the auto-implemented factory goodness we have been enjoying.

The basic concept is to allow the factory extensions to work with methods (func or auto-implemented interface method contracts) that return a result of Task.

public class MyClass
{
   public MyClass(int nonServiceDependency, IMyService serviceDependency)
   {
      ...
   }
}

public class IMyClassFactory
{
   public async Task<MyClass> CreateMyClassAsync(int nonServiceDependency);
}

And usage would look something like.

kernel.Bind<IMyClassFactory>().ToFactory();

var factory = kernel.Get<IMyClassFactory>();
var instanceFromFactory = await factory.CreateMyClassAsync(42);

// or alternatively

var func = kernel.Get<Func<int, Task<MyClass>>>();
var instanceFromFunc = await func(42);

[remogloor]

I think you should be able to extend that behavior quite easily by writing your own InstanceProvider

Pseudo Code:

class AsyncIP : StandardInstanceProvider()
{
    override Type GetType()
    {
        var baseType = base.GetType();
        if (baseType.IsTask) return baseType.GenericArgument[0];
        return baseType;
    }

    override object GetInstance()
    {
        if (ReturnTypeIsTask)
        {
            return GetMethodInfo(Task.Factory.StartNew<>).MakeGenericMethod(this.GetType())
                .Invoke(null, () => base.GetInstance());
        }
        return base.GetInstance();
    }
}