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Subject: Re: [std-proposals] Introduce `operator function`
From: Anders Schau Knatten (anders_at_[hidden])
Date: 2020-02-26 13:44:41


This reminds me of C#'s extension methods, and somewhat of the uniform
function call syntax proposal for C++. Are you familiar with those?

Do you by the way intend for these to have access to private members?

Cheers,
Anders

On Wed, Feb 26, 2020 at 6:02 PM Vishal Oza via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> I am not sure I like this. I can see this as adding functionality to
> classes and struct that were never designed to add functionality to.
> Also how would this interact with classes that derived from A and C or
> using thing like std::tuple or std::pair?
>
> On Tue, Feb 25, 2020 at 2:05 PM Владимир Прокофьев via Std-Proposals <
> std-proposals_at_[hidden]> wrote:
>
>>
>> I have a proposal for the operator of function.
>>
>> Imagine the completed and finished struct which we cannot modify without
>> breaking compatibility.
>>
>> file: a.h
>>
>> struct A
>> {
>> int a1 = 0;
>> int a2 = 0;
>>
>> public:
>> int GetA1() const { return a1; }
>> int GetA2() const { return a2; }
>> };
>>
>> I need to add a new functional for this struct and add a new function to
>> perform some actions under object of this struct:
>> Because struct A is declared in a file which we cannot modify, I have to
>> declare a separate function:
>>
>> int diff(const A& a)
>> {
>> return a.a1 - a.a2;
>> }
>>
>> and use it as like a regular function:
>>
>> A a;
>>
>> int d = diff(a);
>>
>> with the new `operator function` it will look like:
>>
>> // same as
>> // int diff(const &A a)
>> // {
>> // return a.a1 - a.a2;
>> // }
>> operator int(const A& a) diff
>> {
>> return a.a1 - a.a2;
>> }
>>
>> int d = a.diff();
>>
>> This is a sintax sugar, but it helps to make code simpler.
>>
>> It can be confusing with some sort of arguments:
>>
>> operator int(A* a) base
>> {
>> return a->a1 + a->a2;
>> }
>>
>> A *aa = &a;
>> int d = aa.base(); // use `.` notation with a pointer
>>
>> It supports inheritance:
>>
>> struct B : A
>> {
>> int d;
>> };
>>
>> int d = b.diff();
>>
>> ----------
>>
>> The `operator function` brings another kind of object - multiple.
>>
>> struct C
>> {
>> int c;
>> };
>>
>> // same as
>> // int mult(const A& a, const C& c)
>> // {
>> // return a.diff() * c.c;
>> // }
>> operator int(const A& a, const C& c) mult
>> {
>> return a.diff() * c.c;
>> }
>>
>> It can be used when several objects are combined to perform some common
>> action(s):
>>
>> A a;
>> C c;
>>
>> int m = [a,c].mult();
>>
>> auto o = [a,c];
>> int m = o.mult();
>>
>> // work with `o` like with a single object.
>>
>> // int m = mult(a,c);
>>
>> The `*operator function*` allow extending any frozen functional without
>> intervention
>> into the complete code, but it makes code looks like already provides
>> desired functional with
>> additional declaration.
>>
>> With best regards.
>>
>> Vladimir
>>
>> ------------------------------
>>
>> --
>> Std-Proposals mailing list
>> Std-Proposals_at_[hidden]
>> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>>
> --
> Std-Proposals mailing list
> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>



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