Question

So I have a simple method called Invert:

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

It is inside of a static class in a .dll file. Now when I go to a new Winforms project, I add the .dll as a reference and everything is good so far. Now when I do this:

bool test = true;
test.Invert();

I get no errors, but when I do:

MessageBox.Show(test.ToString());

It outputs true, as if nothing has changed. I am not sure if it because of what I am doing in the method or something else. But if I go:

MessageBox.Show((!test).ToString());

It outputs false.

Thanks.

Answer 1

That’s working correctly. Because bool is a value type, it’s passed as a value and the original variable (test) is not ever being changed.

Instead you should do something like:

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

However, creating a method that does what the language does itself is a bit of a waste of time.

I don’t think extension methods will let you take a this parameter by reference, so you would have to use a regular static method, and call it the long way:

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

BooleanHelpers.Invert(ref test);

In the end, it’s going to be a lot cleaner and easier (not to mention more obvious to other developers) to just do it this way:

test = !test;