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Groups > comp.lang.c++ > #69905
| Newsgroups | comp.lang.c++ |
|---|---|
| From | Melzzzzz <Melzzzzz@zzzzz.com> |
| Subject | Re: Substitution failure can be an error |
| References | <qqulj5$jd1$1@dont-email.me> <EGJAF.196091$_i.170118@fx25.am4> <qr0kq0$q0m$1@dont-email.me> |
| Message-ID | <1GXAF.159948$XT1.148145@fx01.am4> (permalink) |
| Organization | usenet-news.net |
| Date | 2019-11-19 19:48 +0000 |
On 2019-11-19, Alf P. Steinbach <alf.p.steinbach+usenet@gmail.com> wrote:
> On 19.11.2019 04:53, Melzzzzz wrote:
>> On 2019-11-18, Alf P. Steinbach <alf.p.steinbach+usenet@gmail.com> wrote:
>>> As the title says, substitution failure can be an error:
>>>
>>>
>>> #include <iostream>
>>> #include <initializer_list>
>>> #include <type_traits>
>>> using namespace std;
>>>
>>> template< class Value >
>>> auto is_in( const initializer_list<Value>& list, const Value v )
>>> -> bool
>>> { return false; }
>>
>> why not just auto? What's the point of both auto and return type?
>
> It may be that you're asking about the syntax.
>
> Well, `auto f() -> T` for /trailing return type/ was introduced in C++11.
>
> Now that you have a name you can look it up.
>
> `auto` for /deduced return type/, like `auto f() { return 3; }` was
> introduced in C++14, almost like sabotage of the C++11 syntax.
>
> Apparently support for `auto auto`, writing `auto f() -> auto { return
> 3; }` in order to specify deduced return type explicitly, was introduced
> in C++17. But of this I'm less sure. Even though compilers I've tried
> accept the syntax I don't even know, 100%, that it's valid C++.
>
> ---
>
> It may alternatively be that you're asking why most C++ programmers
> still generally specify return types instead of using deduced return type.
>
> A deduced return type can be very convenient for e.g. a `begin()` member
> function that just defers the work to some member container's `begin()`.
>
> But a deduced return type can in the worst case mean that you have to
> delve to the bottom of an arbitrary long call chain in order to find out
> what the return type, that the compiler knows, is. On the way you may
> have to do overload resolution and template instantiation just like the
> compiler, to figure out where these calls go. You may have to use a
> debugger.
>
> That's just a waste of time for the programmer.
>
> And so it's strongly counter-productive to use this feature in general.
>
> ---
>
> If you meant the second interpretation, then I think a better question
> is whether there are programmers who regularly use deduced return type,
> and if so, what on Earth makes them do that counter-productive thing?
>
> In my opinion, if they exist, then they're likely a collection of total
> incompetents, the genuinely insane and maybe herd followers, just as
> with any group that does irrational things: some are insane, some don't
> understand any of it, and some (in religion that's most) follow the herd
> in order to derive social advantages, or avoid social disadvantage.
>
> But I would guess that any group of C++ programmers using deduced return
> type is not yet large enough that there would be any herd followers.
Just one question. What's the point of auto then?
>
>
> - Alf
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Substitution failure can be an error "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-11-18 18:49 +0100
Re: Substitution failure can be an error Vir Campestris <vir.campestris@invalid.invalid> - 2019-11-18 21:54 +0000
Re: Substitution failure can be an error Sam <sam@email-scan.com> - 2019-11-18 18:12 -0500
Re: Substitution failure can be an error Melzzzzz <Melzzzzz@zzzzz.com> - 2019-11-19 03:53 +0000
Re: Substitution failure can be an error "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-11-19 12:48 +0100
Re: Substitution failure can be an error Melzzzzz <Melzzzzz@zzzzz.com> - 2019-11-19 19:48 +0000
Re: Substitution failure can be an error "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-11-19 21:31 +0100
Re: Substitution failure can be an error Melzzzzz <Melzzzzz@zzzzz.com> - 2019-11-19 21:20 +0000
Re: Substitution failure can be an error "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-11-19 22:51 +0100
Re: Substitution failure can be an error Melzzzzz <Melzzzzz@zzzzz.com> - 2019-11-19 21:58 +0000
Re: Substitution failure can be an error David Brown <david.brown@hesbynett.no> - 2019-11-20 09:19 +0100
Re: Substitution failure can be an error Öö Tiib <ootiib@hot.ee> - 2019-11-20 02:16 -0800
Re: Substitution failure can be an error scott@slp53.sl.home (Scott Lurndal) - 2019-11-20 14:13 +0000
Re: Substitution failure can be an error Öö Tiib <ootiib@hot.ee> - 2019-11-20 08:34 -0800
Re: Substitution failure can be an error David Brown <david.brown@hesbynett.no> - 2019-11-21 12:34 +0100
Re: Substitution failure can be an error Öö Tiib <ootiib@hot.ee> - 2019-11-21 05:29 -0800
Re: Substitution failure can be an error David Brown <david.brown@hesbynett.no> - 2019-11-21 15:58 +0100
Re: Substitution failure can be an error Christian Gollwitzer <auriocus@gmx.de> - 2019-11-20 11:12 +0100
Re: Substitution failure can be an error Öö Tiib <ootiib@hot.ee> - 2019-11-20 04:25 -0800
Re: Substitution failure can be an error Öö Tiib <ootiib@hot.ee> - 2019-11-20 06:05 -0800
Almost Always Auto? (was Re: Substitution failure can be an error) Vir Campestris <vir.campestris@invalid.invalid> - 2019-11-22 21:46 +0000
Re: Almost Always Auto? (was Re: Substitution failure can be an error) Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-11-23 09:29 +0000
Re: Almost Always Auto? (was Re: Substitution failure can be an boltar@nowhere.co.uk - 2019-11-23 17:23 +0000
Re: Almost Always Auto? (was Re: Substitution failure can be an error) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-28 12:46 -0800
Re: Almost Always Auto? (was Re: Substitution failure can be an error) "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-11-24 00:26 +0100
Re: Almost Always Auto? (was Re: Substitution failure can be an error) "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-11-24 00:28 +0100
Re: Almost Always Auto? (was Re: Substitution failure can be an error) "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-11-24 00:45 +0100
Re: Almost Always Auto? (was Re: Substitution failure can be an boltar@nowhere.co.uk - 2019-11-24 10:47 +0000
Re: Almost Always Auto? (was Re: Substitution failure can be an Melzzzzz <Melzzzzz@zzzzz.com> - 2019-11-24 13:37 +0000
Re: Almost Always Auto? (was Re: Substitution failure can be an boltar@nowhere.co.uk - 2019-11-25 11:08 +0000
Re: Substitution failure can be an error Manfred <noname@add.invalid> - 2019-11-20 18:46 +0100
Re: Substitution failure can be an error "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-11-21 06:02 +0100
Re: Substitution failure can be an error Manfred <noname@add.invalid> - 2019-11-21 15:50 +0100
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