[einpoklum]

> Overloading the Comma Operator Is Powerful

Clearly, it's over 9000!

... more seriously though, overloading the comma operator is a bad idea and you shouldn't do it. In fact, almost nobody does it.

Specifically, you don't want to break the principle of least astonishment with a command such as

    v+= 1,2,3,4,5;

Assuming you want to add up a bunch of literals, what you could do is something like:

   std::array data { 1,2,3,4,5 };
   v += std::reduce(data.begin(), data.end());

and if you've implemented some <algorithm> and <numeric> wrappers for containers, you would have something like an

    template<class Container>
    typename Container::value_type 
    reduce(const Container& container);

and then you would write

   v += reduce(std::array{ 1,2,3,4,5 } );

which is terse and much clearer.

[jzwinck]

An even more concise form is built in, and I think more obvious to readers:

    v.insert(v.end(), { 1, 2, 3, 4, 5 });

[einpoklum]

I was actually not describing adding elements to a container, but adding up values.

[owl57]

See? That's the problem with arithmetic on containers. Python has that already:

    v += 4, 5, 6

Comma doesn't do weird shit: that's just a tuple of numbers. But "+=" then does weird shit: it means concatenation when v is a standard library list, and element-wise addition when v is a numpy vector.