How to detect if a type is a Func and get the type of the T

Question

I am wondering whether I can upgrade a basic IoC container I am using to support lazy load. So if I have registered IFoo, I would like the IoC container to know how to fulfil both of the following dependencies (the first being the standard way IoC containers work, while the second returns a simple delegate that calls into the container for an IFoo when it is invoked).

public Bar(IFoo x)

public Bar2(Func<IFoo> lazyFoo)

The problem comes when I try to write the code that will actually do this. Is there a syntax that will make the following pseudo-code compile?

public T Resolve<T>()
{
    if (T is Func<X>)
        return (T) () => Resolve(typeof(X));
    return (T)Resolve(typeof(T));
}

Or to put my question another way, if I have a type T, how can I detect if it is an instance of Func<X>, and if so, what is the type of X?

score 3 · Accepted Answer · edited May 23 '17 at 12:01

3

take a look at this question from this morning - might give you a good start - C# generic list <T> how to get the type of T?

edited May 23 '17 at 12:01

Community

1
1

answered Jun 25 '09 at 22:01

Scott Ivey

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Indeed, replace `List` with `Func` and you're done... – Marc Gravell Jun 25 '09 at 22:05
yes, looks like this will do it for me. thanks Now I have a problem that the compiler won't let me cast from () => Resolve(theArgumentType) back to the original T (even if I try to cast to object first). "Cannot convert lambda expression to type 'T' because it is not a delegate type" – Mark Heath Jun 25 '09 at 22:13

score 1 · Answer 2 · answered Jun 26 '09 at 12:19

1

I misunderstood your question.

It is impossible to do it in one function the way you're trying to because the compiler must have a delegate type to create the lambda as at compile time.

However, this should work.

public T Resolve<T>()
{
    return (T)Resolve(typeof(T));
}

public Func<T> LazyResolve<T>()
{
    return () => Resolve<T>();
}

answered Jun 26 '09 at 12:19

SLaks

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ok I think I understand why its not possible. Shame, because it would be a nice feature for an IoC container. – Mark Heath Jun 26 '09 at 15:16

score 0 · Answer 3 · answered Jun 25 '09 at 22:21

0

In answer to the question in the comment, you need to invoke the lambda expression, not cast it.

answered Jun 25 '09 at 22:21

SLaks

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I don't want to invoke it yet, I want to pass the Func itself back so that the caller can invoke it when they are ready to – Mark Heath Jun 26 '09 at 05:52
Then you need to cast it to Func. – SLaks Jun 26 '09 at 12:13
I misunderstood; see second answer. – SLaks Jun 26 '09 at 12:20

How to detect if a type is a Func and get the type of the T

3 Answers3