C＃用扩展方法改变一个值

Question

If I have the following extension methods:

internal static class Extensions
{
    public static void Increase(this uint value)
    {
        value += 1;
    }

    public static void Decrease(this uint value)
    {
        if (value > 0) value -= 1;
    }
}

Why does this not result in a changing i to 1?

uint i = 0;
i.Increase();

Answer 1

The parameter is being passed by value, that's all. There's nothing special about extension methods on this front. It's equivalent to:

Extensions.Increase(i);

You'd need the method to have the first parameter passed by reference (with ref ) for that to have any effect... and that's prohibited for extension methods anyway.

So while you could write a method allowing you to call it as:

Extensions.Increase(ref i);

you won't be able to make that an extension method.

An alternative is to make the method return a value, at which point you could have:

i = i.Increase();

If you're not entirely clear on pass-by-reference vs pass-by-value semantics, you might want to read my article on the topic .