Optional parameters on delegates doesn't work

问题:

This question already has an answer here:

• Can a Delegate have an optional parameter? 2 answers

Why this piece of code does not compile?

delegate int xxx(bool x = true);

xxx test = f;

int f()
{
   return 4;
}

回答1:

Optional parameters are for use on the calling side - not on what is effectively like a single-method-interface implementation. So for example, this should compile:

delegate void SimpleDelegate(bool x = true);

static void Main()
{
    SimpleDelegate x = Foo;
    x(); // Will print "True"
}

static void Foo(bool y)
{
    Console.WriteLine(y);
}

回答2:

What will happen test(false)? It will corrupt the stack, because signatures must match.

回答3:

Try this way:

static int f(bool a)
{
  return 4;
}

回答4:

Because optional parameters do not change the underlying signature of the method, which is important to delegates.

What your code is expecting is the optional parameter to not be in the method signature if you don't use it - this is incorrect.