220 30773 article Path: news.gmane.org!.POSTED!not-for-mail From: "Vicente J. Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Make Typedef Great Again Date: Sun, 5 Feb 2017 11:41:32 +0100 Lines: 1001 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="------------5CA4DAA407AE010D0050BCCF" X-Trace: blaine.gmane.org 1486291295 15527 195.159.176.226 (5 Feb 2017 10:41:35 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 5 Feb 2017 10:41:35 +0000 (UTC) User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDH67CONY4PBBXUC3TCAKGQE3FLTGUQ@isocpp.org Sun Feb 05 11:41:30 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f70.google.com ([209.85.215.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1caKGA-0003rA-Cn for gclcip-std-proposals@m.gmane.org; Sun, 05 Feb 2017 11:41:30 +0100 Original-Received: by mail-lf0-f70.google.com with SMTP id o12sf23945624lfg.7 for ; Sun, 05 Feb 2017 02:41:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:x-original-sender:x-original-authentication-results :reply-to:precedence:mailing-list:list-id:x-spam-checked-in-group :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=J+isQSVzQB7eDnSxfEMWShjK+bkZw7CeMLjgNWN2sEw=; b=s+cvlpHUtIYpOF26p+S99C8tV0uODlD5oKd3kqKeP5NceEbLPje6sX+gKBkEG6KsMv Eb5NEJQA/tUrCLqLPcldsGW0soLl0WMQQIS34M4kOX1mnu1vs6KMpMkD8NAdtakOTD9M W9S6+Ezfe83PPT8lPyEoBi+1btOT7SwcW1iIAMx2RI8SeR5ciTpU3wADwHw/qE+UvdcV ETYLWHLXGzVswVU2oTbtMBzytViU1vhkHpb6gux9oDy6lqSGxMnOu+cLH7RTG6O//cbt pToEe0vJoYm0ixu5xYMjtgD0g7jxNc5IoYHrhhmP7snz25ci0j28hvkBDlNzoDDs+bIQ U2IQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=J+isQSVzQB7eDnSxfEMWShjK+bkZw7CeMLjgNWN2sEw=; b=sYcjj8czdV+375/OrUb5VgJ1JzJ9lDNh/Rj2ecsnaZNgUqaEgButn0B5wLn0xNz/ri NaxKz2OETmeMAli4WSUFUarzEyd/95Hn639IgouIF1KcYlqzLbUAfDwqwJQsxwERwXp5 AVWIa/XUAwNyrSNUkMQAz1VUhbrCRN6g5/bUuBWm0p2CGOVpvcN8wNqOfaB1iG9ropmL w2vixyCTvQ+c32niJVWXdq/pY9IH9AHDBxCOSoNyiJyL83Vq02vsUijVqFxHEz1sGLuw zheBt/C3EFKQk6fjOH/iyRslD8YfjxEMdov2qG3btxrvvYCLd5tJLR1yt92Cyrl18UVr OJAg== X-Gm-Message-State: AMke39kJJ/lEQck/npV6tS7p49gXRSmPW6C5Q8FHt35aeVqSfM/q677bb2HN986a7BCXRQ== X-Received: by 10.25.198.11 with SMTP id w11mr441429lff.5.1486291296127; Sun, 05 Feb 2017 02:41:36 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.98.5 with SMTP id w5ls758389wmb.27.canary-gmail; Sun, 05 Feb 2017 02:41:34 -0800 (PST) X-Received: by 10.223.135.163 with SMTP id b32mr4913792wrb.184.1486291294675; Sun, 05 Feb 2017 02:41:34 -0800 (PST) Original-Received: from smtp.smtpout.orange.fr (smtp04.smtpout.orange.fr. [80.12.242.126]) by mx.google.com with ESMTPS id b40si37977044wrb.87.2017.02.05.02.41.34 for (version=TLS1 cipher=AES128-SHA bits=128/128); Sun, 05 Feb 2017 02:41:34 -0800 (PST) Received-SPF: neutral (google.com: 80.12.242.126 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.126; Original-Received: from imac-de-vicente-botet-escriba.home ([2.11.72.89]) by mwinf5d60 with ME id gyhY1u0101vahZu03yhZRz; Sun, 05 Feb 2017 11:41:34 +0100 X-ME-Helo: imac-de-vicente-botet-escriba.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Sun, 05 Feb 2017 11:41:34 +0100 X-ME-IP: 2.11.72.89 In-Reply-To: X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.126 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) smtp.mailfrom=vicente.botet@wanadoo.fr Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:30773 Archived-At: This is a multi-part message in MIME format. --------------5CA4DAA407AE010D0050BCCF Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Le 26/12/2016 =C3=A0 08:38, TONGARI J a =C3=A9crit : > Typedef declaration is superseded by type alias declaration since=20 > C++11, its legend seems to come to the end. However, we can make=20 > typedef much more useful than it is, by allowing it to be used in=20 > accompany with variable declarations (including parameters and return=20 > types) and base-clause in a class declaration. > > The problem > > Everyone who loves templates are likely to face a problem - the name=20 > of the type being specified is too long that we don't want to spell it=20 > out twice! > Although we have type alias, but unfortunately in many cases, it=20 > cannot be used at the first place and we are forced to spell the=20 > irritating names at least twice if we have to refer to the type more=20 > than once. > Here are some examples: > > In function return type: > | > template > typenameMetaFunc::type f() > { > usingT =3DtypenameMetaFunc::type;// yuck! > // Use `T` from now on... > } > | > > In base-clause: > | > template > classDerived:publictypenameMetaFunc::type > { > usingBase=3DtypenameMetaFunc::type;// yuck! > // Use `Base` from now on... > } > | > > In parameter list: > | > template > voidf(SomeTemplatea,SomeTemplateb/*yuck!*/); > | > > In deduced type: > | > auto&ref=3DgetSomeRef(...); > usingT =3Dstd::remove_reference_t;// yuck! > // Use `T` from now on... > | > > Evidence > > These discussions on the std-proposals list are also arose from the=20 > same problem: > > * Named base classes > > * decltype(return) > > > > The solution > > The problem comes from the inability to declare the type alias at the=20 > first place, and the solution is gonna to enable it - with the=20 > extended typedef. > > In function return type: > | > template > typedeftypenameMetaFunc::type T f()// yay! > { > // Use `T` from now on... > } > | > I'm not saying the feature is not needed. I believe however that the=20 proposal needs to compare what it is currently doable. Couldn't we use the existing language already | template::type |= > T f()// yay! { // Use `T` from now on... } | > In base-clause: > | > template > classDerived:typedefpublictypenameMetaFunc::type Base// yay! > { > // Use `Base` from now on... > } > | > | template::type|= > classDerived:publicBase// yay! { // Use `Base` from now on... } | > Note how the occurrence of /access-specifier/ in base-clause differ in=20 > semantic: > | > classC :typedefT B // T: private base; B: private typedef > classC :typedefpublicT B // T: public base; B: private typedef > classC :publictypedefT B // T: private base; B: public typedef > classC :publictypedefpublicT B // T: public base; B: public typedef > | > > In parameter list: > | > template > voidf(typedefSomeTemplateT a,T b);// yay! > | > I'm not sure the |blahblahcould be inferred Do tou mean | |template voidf(U, typedefSomeTemplateT a,T b); If it is the case | ||template|| > voidf(U, T a,T b); See |http://melpon.org/wandbox/permlink/FBlKcQZwxAs5ZJRT | > In deduced type: I have not alternative to this with the current language :( Vicente --=20 You received this message because you are subscribed to the Google Groups "= ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/b1ae66d2-da65-bd04-6ac0-8bed1d13c5c5%40wanadoo.f= r. --------------5CA4DAA407AE010D0050BCCF Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Le 26/12/2016 =C3=A0 08:38, TONGARI J a =C3=A9crit=C2=A0:
Typedef declaration is superseded by type alias declaration since C++11, its legend seems to come to the end. However, we can make typedef=C2= =A0much more useful than it is, by allowing it to be used in accompany with variable declarations (including parameters and return types) and base-clause in a class declaration.

The problem

Everyone who loves templates are likely to face a problem - the name of the type being specified is too long that we don't want to spell it out twice!
Although we have type alias, but unfortunately in many cases, it cannot be used at the first place and we are forced to spell the irritating names at least twice if we have to refer to the type more than once.
Here are some examples:

In function return type:
template<blahbla= h...>=
typename MetaFun= c<blahbla= h...>= ::type f<= /span>()
{
=C2=A0 =C2=A0 using T =3D typenam= e MetaFun= c<blahbla= h...>= ::type; // yuck= !
=C2=A0 =C2=A0 // Use `T` from now on...
}

In base-clause:
template<blahbla= h...>=
class Derived= : public<= /span> typenam= e MetaFun= c<blahbla= h...>= ::type {
=C2=A0 =C2=A0 using Base =3D typenam= e MetaFun= c<blahbla= h...>= ::type; // yuck= !
=C2=A0 =C2=A0 // Use `Base` from now on...
}

In parameter list:
template<blahbla= h...>=
void f(SomeTem= plate<blahbla= h...>= a, SomeTem= plate<blahbla= h...>= b/*yuck!= */);

In deduced type:
auto& ref =3D getSomeRef(...);
using T =3D std::remove_= reference_t<decltyp= e(ref)>;<= /span> // yuck= !
// Use `T` from now on...

Evidence

These discussions on the std-proposals list are also arose from the same problem:

The solution

The problem comes from the inability to declare the type alias at the first place, and the solution is gonna to enable it - with the extended type= def.

In function return type:
template<blahbla= h...>=
typedef typenam= e MetaFun= c<blahbla= h...>= ::type T = f() // yay!=
{
=C2=A0 =C2=A0 // Use `T` from now on...
}

I'm not saying the feature is not needed. I believe however that the proposal needs to compare what it is currently doable.

Couldn't we use the existing language already

template<= blahblah..., typename T =3D = typenam= e MetaFun= c<blahbla= h...>= ::type >
= T f() // yay!
= {
=C2=A0 =C2=A0 // Use `T` from now on...
= }
In base-clause:
template<blahbla= h...>=
class Derived= : typedef= public<= /span> typenam= e MetaFun= c<blahbla= h...>= ::type Base // yay!=
{
=C2=A0 =C2=A0 // Use `Base` from now on...
}


template<= blahblah..., typename Base=3D= typenam= e MetaFun= c<blahbla= h...>= ::type>
= class Derived : public Base= // yay!
= {
=C2=A0 =C2=A0 // Use `Base` from now on...
= }

Note how the occurrence of access-specifier=C2=A0in base-clause differ in semantic:
class C : typedef= T B // T: private base; B: private typedef
class C : typedef= public<= /span> T B // T: public base; B: private typedef
class C : public<= /span> typedef= T B // T: private base; B: public typedef
class C : public<= /span> typedef= public<= /span> T B // T: public base; B: public typedef

In parameter list:
template<blahbla= h...>=
void f(typedef= SomeTem= plate<blahbla= h...>= T a, T b); // yay!=

I'm not sure the blahblah could be inferred

Do tou mean


template<class U>
void= f(U, typedef<= span style=3D"color: #000;" class=3D"styled-by-prettify"> SomeTemplate<U> T a, T b);

If it is the case


template<class U= , class T = =3D Som= eTemplate<= ;U>= ; >
= void f(U, = T a<= span style=3D"color: #660;" class=3D"styled-by-prettify">, T b= );

See=C2=A0 http://melpon.org/= wandbox/permlink/FBlKcQZwxAs5ZJRT
In deduced type:
I have not alternative to this with the current language :(

Vicente

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