Using "ref" or "out" in a extension

Question

anyone knows a way to solute this smart?

public static void Invert(this ref bool value)
{
    value = !value;
}

c# says i can not use "ref" or "out" within an extension. But such extensions like List.Clear() exist.

`List.Clear()` is not an extension method and doesn't take `ref` or `out` arguments. What are you asking exactly? — Frédéric Hamidi, Jul 18 '12 at 09:59
No, the first argument to an extension method **cannot** be `ref` or `out`. — Marc Gravell, Jul 18 '12 at 11:11

score 7 · Accepted Answer · answered Jul 18 '12 at 10:01

List.Clear() isn't an extension method, it's a method. And even if it was an extension method, it wouldn't need to receive the parameter as ref, because it doesn't "return" a different list than the one you had, it modifies the list.

And, in general, you can't. But you normally don't need to.

What about:

public static bool Invert(this bool value)
{
    return !value;
}

bool x = false.Invert();

score 4 · Answer 2 · answered Jul 18 '12 at 10:01

First of all, I know of no List.Clear extension method. List<T>.Clear() is a normal method. It has no ref parameters.

The second issue is that List<T> is a mutable reference type. So you can modify it, without changing the reference itself. You only need ref if you want to change the reference itself, or if you're working on a value type.

Using "ref" or "out" in a extension

2 Answers2