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Re: [std-proposals] explicit keyword (new use)

From: Tatsuya Yanagita <hemogurobin.711_at_[hidden]>
Date: Tue, 3 May 2022 21:00:53 +0900
Is explicit exactly same as =delete?
I think they get different results with a brace initializer:

void f(int);
void f(auto) = delete;

void g(explicit int);

int main() {
  f({}); // OK
  g({}); // ERROR
  g(int{}); // OK
}

2022年5月3日(火) 18:42 Bo Persson via Std-Proposals <
std-proposals_at_[hidden]>:

> On 2022-05-03 at 09:23, Abdullah Qasim via Std-Proposals wrote:
> > But learning it, & understanding it takes 30 sec.
> >
> > Instead of:
> >
> > “What are these functions deleted?”
> >
> > Why not:
> > “Oh, ok, these are explicit types!”
>
>
> So then we have to wonder "this library has deleted member functions,
> but that library uses explicit types. Why did they do that? What is the
> difference? None?!".
>
>
> >
> > *From: *Jens Maurer via Std-Proposals
> > <mailto:std-proposals_at_[hidden]>
> > *Sent: *03 May 2022 12:22
> > *To: *Abdullah Qasim via Std-Proposals
> > <mailto:std-proposals_at_[hidden]>
> > *Cc: *Jens Maurer <mailto:Jens.Maurer_at_[hidden]>
> > *Subject: *Re: [std-proposals] explicit keyword (new use)
> >
> > On 03/05/2022 08.51, Abdullah Qasim via Std-Proposals wrote:
> > > But here is the thing:
> > >
> > >
> > >
> > > Why not make code simpler??
> >
> > Because it requires everybody to learn a new wrinkle of
> > the language. That cost has to be weighed against the
> > perceived increase in simplicity.
> >
> > Jens
> >
> >
> > > Why write multiple “= delete” functions, conscientiously tracking all
> > conversions, when explicit inside functions is much simpler??
> > >
> > >
> > >
> > > Also, someone suggested explicit template parameters, like this:
> > >
> > >
> > >
> > > *template <explicit typename T>*
> > >
> > >
> > >
> > > Why not have consistence, & allow:
> > >
> > >
> > >
> > > *int func (explicit int x, int y)*
> > >
> > >
> > >
> > > as well?
> > >
> > >
> > >
> > > *From: *Jason McKesson via Std-Proposals
> > <mailto:std-proposals_at_[hidden]
> > <mailto:std-proposals_at_[hidden]>>
> > > *Sent: *01 May 2022 22:07
> > > *To: *std-proposals_at_[hidden]
> > <mailto:std-proposals_at_[hidden]
> > <mailto:std-proposals_at_[hidden]>>
> > > *Cc: *Jason McKesson <mailto:jmckesson_at_[hidden]
> > <mailto:jmckesson_at_[hidden]>>
> > > *Subject: *Re: [std-proposals] explicit keyword (new use)
> > >
> > >
> > >
> > > We have `= delete` for removing unwanted conversions. Indeed, you can
> > > basically force the use of `int` with:
> > >
> > > template<typename T>
> > > int func (int, T) = delete;
> > >
> > > Any call to `func` that doesn't pass an `int` as the second parameter
> > > will fail to compile. Even things convertible to `int` will not be
> > > used.
> > >
> > > If you want to allow more things to call it, you can only cull out
> > > floating-point types with this overload:
> > >
> > > int func(int, double) = delete;
> > >
> > > Calling func(5, 1) will work, but func(5, 3.4) or even func(5, 2.3f)
> > > will fail. This preserves the ability to call it with types
> > > convertible to `int` (but those which are convertible to `int` *and*
> > > floats will fail due to ambiguity).
> > >
> > > On Sun, May 1, 2022 at 3:57 AM Abdullah Qasim via Std-Proposals
> > > <std-proposals_at_[hidden]> wrote:
> > >>
> > >>
> > >>
> > >> int func (int var, explicit int select_menu)
> > >>
> > >> {
> > >>
> > >> /// ...
> > >>
> > >> }
> > >>
> > >>
> > >>
> > >> Why would I want user to put a double value in select_menu ???
> > >>
> > >>
> > >>
> > >> Also, why would I want to disallow a double in var ???
> > >>
> > >>
> > >>
> > >> The solution:
> > >>
> > >> Allow explicit in param list!!
> > >>
> > >>
> > >>
> > >> Not too hard to implement, either.
> > >>
> > >> --
>
>
> --
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> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>

Received on 2022-05-03 12:01:06