Re: "auto" operators syntax

"ThosRTanner" <>
Fri, 30 Jun 2006 07:54:27 CST
Andrei Polushin wrote:


Most user-defined operators should have well-known semantics, so they
are implemented by pattern, written so many times by many people.
It might be quite annoying for experts, and error-prone for novices.

They have well defined semantics in certain situations, and in those
situations, I agree the lack of compiler support is really aggravating.

I propose to allow operators with "auto" modifier, so that compiler is
able to provide predefined implementation for them.

It looks like the following:

    class A {
        int first;
        int second;
        A(int first, int second) auto;

        A& operator+=(const A& a) auto;
        static A operator+(const A& a, const A& b) auto;

        A& operator++() auto;
        A operator++(int) auto;

        bool operator==(const A& a) const auto;
        bool operator!=(const A& a) const auto;

        bool operator<(const A& a) const auto;
        bool operator>(const A& a) const auto;
        bool operator>=(const A& a) const auto;
        bool operator<=(const A& a) const auto;

The code to be generated is shown in /*...*/ comments:

    class A {
        int first;
        int second;
        A(int first, int second) auto;
            : first(first), second(second) {}

Well, I can sort of see this, but I write very few classes where the
only private data members are those initialised by the constructor.

There's probably some sort of argument for just having
       A(...) auto; //Equivalent to a(int first_, int second_) :
first(first_), second(second_)

        A& operator+=(const A& a) auto;
            first += a.first;
            second += a.second;
            return *this;

This is not necessarily an intuitive implementation - OK for complex,
but for other things?

You should have also listed all the standard arithmetic operators.


        A& operator++() auto;
            return *this;

I cannot believe this to be the case for any class with more than one
data member. I think A& operator++() { *this += 1; return *this } might
be more useful.

        bool operator<(const A& a) const auto;
            return first < a.first
                || first == a.first && second < a.second

Umm. This doesn't seem to be compatible with your ++.

Anyway, IIRC, there are some templates in boost that allow you to do
that sort of thing.

In addition, the same syntax should be allowed for main():

    int main() auto;
        Do what I mean

How on earth is the compiler meant to work out what you want to do?

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