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Subject: Re: [std-proposals] Flexible function parameters
From: Arthur O'Dwyer (arthur.j.odwyer_at_[hidden])
Date: 2020-07-09 09:01:50


On Thu, Jul 9, 2020 at 9:32 AM Jake Arkinstall via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> The why is clear.
>

FWIW, no it's not. The OP didn't give any reason for the new syntax at all.
In fact, the OP didn't even say what the new syntax is supposed to *do!*
What is `void f(int x, int y) {}` supposed to do differently from `void
f(int x; int y) {}` or `void f(int x: int y) {}`? Explaining *what the
change does* is an important part of any change request.

> It's a way of forming groupings of parameters, which currently isn't
> possible without bringing structs into the equation. This opens up some
> decent possibilities: Defaults can apply to the group (rather than having
> to put them at the end of the call), parameter packs can be logically
> separated in a way they currently cannot, and so we can pass multiple
> parameters to operator[] without interfering with the comma operator.
>

FYI, there's already a deploy plan in motion (to the admittedly limited
extent that WG21 can be said to make "deploy plans") to get multi-parameter
`operator[]` overloads. The first step in the plan was committed in C++20:
http://eel.is/c++draft/depr.comma.subscript
The second step, targeted for C++23, is to support overloaded
`operator[](int x, int y)` (or whatever parameter types) with the natural
meaning and call syntax.
The goal and justification, targeted also for C++23 as far as I know, is to
finally ship `mdspan`. (Which I personally think is a silly end goal, but
there seem to be a lot of people looking forward to it just as a lot of
people look forward to C++20's `span`.)

–Arthur



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