Is Func<T, TResult> a special delegate or can we create it manually also?

Func<T, TResult> delegate is for a delegate with a single param and return type of TResult.

Is this a special delegate or is it something 开发者_如何学编程we can code ourselves manually?

e.g. could I create a Func<T, TResult> but that accepts 2 input params?

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"Func" is actually a family of classes in the System namespace, namely:

Func<TResult> (0 params), Func<T,TResult> (1 param), Func<T1,T2,TResult> (2 params) ... Func(17) (16 params).

There are 17 different "Func" classes total, supporting from 0 to 16 parameters. It is allowable for them to share the name in code ("Func") even though they are actually different types (Func, Func', Func'', etc) thanks to how Generics work in .NET -- the number of generics determines/disambiguate which actual type is used.

Happy coding.

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As far as converting between delegates, this may be of use (runs in LINQPad, "C# Program"):

delegate int MyDelegate (int y);

void Main()
{
    Func<int,int> fun1 = (q) => q * q;
    MyDelegate del = new MyDelegate(fun1); // Convert the "Func" delegate to custom...
    Func<int,int> fun2 = new Func<int,int>(del); // ...and back
}

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There's already a Func<TParam1, TParam2, TResult> that does this. But what you're asking for is a little different (you know that both parameters are the same type). You can still use the same type parameter twice with the built-in Func, but if you really want to you could do this:

public delegate TResult MyFunc<T, TResult>(T param1, T param2);

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There's already a Func<T1, T2, TResult> that accepts two input parameters.

To answer your question though, no, it's not special compared to any other delegate, and you could create your own, but why would you?

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You shouldnt have to create your own Func. There are overloads for Func that go up to 16 args.

http://msdn.microsoft.com/en-us/library/dd402862.aspx

and every variation in between. Essentially, the first n-1 args are input and the last is the return value.

So, Func<int,int,int,int> compares to a delegate that takes 3 int args and returns int.