Question

I just got this error when trying to use a function parameter for a return value.
I could only find answers to related issues but not this one.

Example:

void someNumber(int foo)
{
  foo = 3;
}

int bar;
someNumber(bar);

What’s the problem here?

Answer 1

As it turns out C# is a bit weird in this respect but better weird than C/C++. 🙂

If you pass a reference only for the output value you have to make that explicit in this way:

void someNumber(out int foo)
{
  foo = 3;
}

int bar;
someNumber(out bar);

So while you still have an output parameter in the input parameter list (at least that’s what it is in my head) at least it is now blatantly obvious.

Note that it is now an error NOT to assign to foo in the body of someNumber. It’s kind of like an anti-const, which would obviously have been a much cooler keyword. 😉