Why must C# operator overloads be static?

问题:

Why does C# require operator overloads to be static methods rather than member functions (like C++)? (Perhaps more specifically: what was the design motivation for this decision?)

回答1:

Take a look at this post.

A couple of reasons, the primary seeming to be to preserve operator symmetry (such that the left hand side of a binary operation does not get special treatment, as being responsible for dispatching the operation).

回答2:

Answered in excruciating detail here:

http://blogs.msdn.com/ericlippert/archive/2007/05/14/why-are-overloaded-operators-always-static-in-c.aspx

There is also another subtler point about value types and instance operators. Static operators make this kind of code possible:

class Blah {

    int m_iVal;

    public static Blah operator+ (Blah l, int intVal)
    {
        if(l == null)
            l = new Blah();
        l.m_iVal += intVal;
        return l;
    }
}

//main
Blah b = null;
b = b + 5;

So you can invoke the operator, even though the reference is null. This wouldn't be the case for instance operators.

回答3:

Perhaps its best to think why should the methods not be static. There is no need for state and hence this.