没有类的重载operator- =

Question

Is it possible to overload -= like this without it being a method of a class?

vector<int>& operator-=(int a, int b){
    vector<int> v;
    v.push_back(a); v.push_back(b);
    return v
}

I have a line in a homework assignment that looks something like this:

SomeStructure-=1-=2-=3;

What it is supposed to do is remove the elements with the indexes 1, 2 and 3 from the structure(in that order).

It seems like the option I tried above is not possible (I was thinking of collecting all the indexes in a vector and then removing them from the structure one by one). Is there some other way to do this?

Answer 1

The assignment operator is right to left associative.

From the C++ Standard

5.17 Assignment and compound assignment operators [expr.ass]

1 The assignment operator (=) and the compound assignment operators all group right-to-left.

So this expression

SomeStructure-=1-=2-=3;

is in any case invalid because you may not write

2 -= 3;

And you may not overload operators for built-in types.

I advice to write simply a function for example with name erase which will have parameter of type std::initializer_list In this case you could write

SomeStructure.erase( { 1, 2, 3 } );

Answer 2

重载运算符时，作为参数传递的至少一种类型必须non primitive type ，这不是您的情况，这就是为什么我们通常inside classes重载运算符inside classes而很少将其作为global functions重载。