Func / Action delegates with reference arguments/p

问题:

I just wondered, how the exact syntax is for ref and out parameters for delegates and inline lambda functions.

here is an example

if a function is defined as

 public void DoSomething(int withValue) { } 

a delegate in a function can be created by

 public void f()
 {   
     Action<int> f2 = DoSomething;
     f2(3);
 }

how is that syntax, if the original function would be defined as

 public void DoSomething(ref int withValue) { withValue = 3; } 

回答1:

You need to define a new delegate type for this method signature:

delegate void RefAction<in T>(ref T obj);

public void F()
{
    RefAction<int> f2 = DoSomething;
    int x = 0;
    f2(ref x);
}

The reason why the .NET Framework does not include this type is probably because ref parameters are not very common, and the number of needed types explodes if you add one delegate type for each possible combination.

回答2:

You can't use Action, Func<T>, or the built-in delegates, but need to define your own in this case:

delegate void ActionByRef<T>(ref T value);

Then, given this, you can have:

int value = 3;
ActionByRef<int> f2 = DoSomething;
f2(ref value);