C++ Logo

STD-PROPOSALS

Advanced search

Subject: Re: [std-proposals] New attribute to change the default specifiers and qualifiers
From: Brian Bi (bbi5291_at_[hidden])
Date: 2021-01-19 15:38:53


On Tue, Jan 19, 2021 at 2:28 PM Bo Persson via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> On 2021-01-19 at 15:35, Vinícius Costa via Std-Proposals wrote:
> > Hi!
> >
> > I'd like to propose a new attribute to change the default specifiers and
> > qualifiers in a given scope.
> >
> > Often there's a lot of boilerplate code involved because the default
> > specifiers and qualifiers are not the "correct" ones (stress on the
> > quotation marks).
> > So we need to explicitly make variables const, functions const, noexcept
> > or final, etc.
> >
> > It would be a lot simpler to have a way to switch the default specifiers
> > and qualifiers, making them more permissive or stricter.
> >
> > The idea is to create an attribute that would apply to a scope. With
> > that, we won't mess with back-compatibility and it would allow an easy
> > migration towards the new standard.
> > Furthermore, it would help to enforce some good practices like
> > const-correctness.
> >
> > For example, the following two codes will be the same.
> >
> > namespace example [[strict]] {
> > class Foo : public Bar
> > {
> > void do_it(double *ptr) override
> > {
> > int x = /* some initialization code here*/
> > /* more code here */
> > }
> > };
> > }
> >
> > namespace example {
> > class Foo final : public Bar
> > {
> > void do_it(double * __restrict ptr) const noexcept override final
> > {
> > const int x = /* some initialization code here*/
> > /* more code here */
> > }
> > };
> > }
> >
>
> The committee seems to not want attributes to change the meaning of
> programs. If a compiler ignores [[noreturn]] or [[nodiscard]] or
> [[gnu::special]], the program still works the same (although perhaps
> using less optimal code).
>

I've been told that the rule about attributes is not "attributes cannot
change the meaning of programs" but rather "an implementation that ignores
the attribute can still be conforming". So you can have a weak form of
[[strict]]: the compiler can be allowed to warn if a variable's value is
modified or bound to a non-const reference.

>
> Here [[strict]] really affects the meaning!
>
> Also, if I want all the specifiers - except final - how do I do that? :-)
>
>
> Bo Persson
>
>
> --
> Std-Proposals mailing list
> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>

-- 
*Brian Bi*


STD-PROPOSALS list run by std-proposals-owner@lists.isocpp.org

Standard Proposals Archives on Google Groups