220 30779 <7aa018bf-dcaa-6c95-dd64-413990592c37@wanadoo.fr> 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 14:56:35 +0100 Lines: 540 Approved: news@gmane.org Message-ID: <7aa018bf-dcaa-6c95-dd64-413990592c37@wanadoo.fr> References: <3fbbd6b8-9087-4c02-bf66-632b7eff480d@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="------------D4F2F8D6BC7572938EFADC2F" X-Trace: blaine.gmane.org 1486302997 5878 195.159.176.226 (5 Feb 2017 13:56:37 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 5 Feb 2017 13:56:37 +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+bncBDH67CONY4PBBFO63TCAKGQEOFZ5YUY@isocpp.org Sun Feb 05 14:56:32 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f71.google.com ([209.85.215.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1caNIu-0001MO-CF for gclcip-std-proposals@m.gmane.org; Sun, 05 Feb 2017 14:56:32 +0100 Original-Received: by mail-lf0-f71.google.com with SMTP id z134sf25331473lff.5 for ; Sun, 05 Feb 2017 05:56:38 -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=+Bm8TrwqPAOQ3l/nA5kq5W9T0gJyGoF8Xo9hEiMmbpg=; b=jeMDOWimHPrMILA8WwYCZfV3KOS8S7fxKELYu7te7Z0HO+b1FAWdg4qforCgeTSZJ1 TcpPtMUeAvswuDXGYFTFB91pZac0TcUN6ExjVOAp+9dqHq76otfj1fdqpePgxaX22x/s nRrAUn8ecNCxv8RmpwrZ43Pjzfx/f8DwYui1FQktcZiILs4PwE1pK5NvkQSWGwdRhzmF qfc277haskGYqCkzRQQVMFGSO28uFeTwby4FwNvnxZelV71cktn28U7Lo4gzuT63JxMY bEo7pzIH/LstS27/vZrGa5GU7dEkFZvVHDMgZu9wQVLNffwCSFFZf7hjRLoADHUDGI1e 4ckg== 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=+Bm8TrwqPAOQ3l/nA5kq5W9T0gJyGoF8Xo9hEiMmbpg=; b=BFm+poOuSssi5hBcsAH/9QUQ75Cb2vm5H9ae1yTfrn5do0744u6BVrQ2acabh8wzcV cnOYfB1m+y5/lkm7j3Nni1ZzyPPMb/rfpmer6aLudXGNFW95ESbSlSi9hIFPswX2d9KU kpJX/btz40+/rMRa2cvhj1lYFFapFp4DqnRznc2AMLeK6kHUBpXCD/mSYSq/LOyfQikx M8OctN+ama4ZefqB1Qyb/jBCNCFBAqQrFgqAxQGe8D4zobLXZsC9DW2eT+16c9stQFmK brNct06CiroK+/P7PNERPa7jpYG6qxdbMI+z/+IP0J268iaj3veNWEl49CS+Gmz0H1+5 oF4w== X-Gm-Message-State: AIkVDXKqo3fJsHDFKAkrN5EZb1MNYRa1nhQzx8SiffA4+5jjji7FbxQIzXz0bUjm0bQXNA== X-Received: by 10.46.21.78 with SMTP id 14mr40274ljv.0.1486302998203; Sun, 05 Feb 2017 05:56:38 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.66.215 with SMTP id k84ls801822wmi.25.canary-gmail; Sun, 05 Feb 2017 05:56:36 -0800 (PST) X-Received: by 10.223.133.131 with SMTP id 3mr5396575wrt.161.1486302996756; Sun, 05 Feb 2017 05:56:36 -0800 (PST) Original-Received: from smtp.smtpout.orange.fr (smtp13.smtpout.orange.fr. [80.12.242.135]) by mx.google.com with ESMTPS id t2si4403186wmt.152.2017.02.05.05.56.36 for (version=TLS1 cipher=AES128-SHA bits=128/128); Sun, 05 Feb 2017 05:56:36 -0800 (PST) Received-SPF: neutral (google.com: 80.12.242.135 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.135; Original-Received: from imac-de-vicente-botet-escriba.home ([2.11.72.89]) by mwinf5d75 with ME id h1wb1u0041vahZu031wbfv; Sun, 05 Feb 2017 14:56:36 +0100 X-ME-Helo: imac-de-vicente-botet-escriba.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Sun, 05 Feb 2017 14:56:36 +0100 X-ME-IP: 2.11.72.89 In-Reply-To: <3fbbd6b8-9087-4c02-bf66-632b7eff480d@isocpp.org> X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.135 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:30779 Archived-At: This is a multi-part message in MIME format. --------------D4F2F8D6BC7572938EFADC2F Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Le 05/02/2017 =C3=A0 14:22, Bengt Gustafsson a =C3=A9crit : > @Vicente: You present some nice solutions for the current language,=20 > but the drawback is of course that it is not obvious that it is=20 > /forbidden/ to change the default value of the parameter. I don't understand, could you clarify? > The other, minor, issue is that the template parameter name is not=20 > usable outside the template itself, which the typedef name would be. Yes, this could be important on the base class case. For this case you=20 could define a nested alias. | template::type|= > classDerived:publicBase// yay! { public: using base_type =3D Base; // Use `Base` from now on... } | Could you show an example where the base type is needed outside the=20 Derived class? > > Nevertheless it is of course advisable to mention theses possibilities=20 > in a future proposal, as you say. > > I see a problem with the proposal in that it has fairly complicated=20 > rules to learn, and the meaning differs depending on where you place=20 > your public's and const's. I'm not sure if the utility of the function=20 > outweighs the extra burden of having to learn and remember these extra=20 > rules. I agree with you here. It is too complex. We just need a name. Vicente > > We also have decltype to solve some of the use cases. > > > Den s=C3=B6ndag 5 februari 2017 kl. 13:56:12 UTC+1 skrev TONGARI J: > > On Sunday, February 5, 2017 at 6:41:36 PM UTC+8, Vicente J. Botet > Escriba wrote: > > 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 |typenameMetaFunc::type |> > T f()// yay! > { > // Use `T` from now on... > } > | > > In this case, it's just an alternative w/o (ab)using the template > param, like how concept-lite tries to eliminate enable_if trick. > > | > template Base=3D|typenameMetaFunc::type|> > classDerived:publicBase// yay! > { > // Use `Base` from now on... > } > | > > This does not work if "blahblah...", is actually a template > parameter pack, which has to be the last one. > >> 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); > | > > > I mean something like: > | > template > voidf(typedefstd::tupleT a,T b); > > f(std::make_tuple(1,2),std::make_tuple(3,4));//Args =3D=3D {int, int}= , > T =3D=3D std::tuple > | > > --=20 > You received this message because you are subscribed to the Google=20 > Groups "ISO C++ Standard - Future Proposals" group. > To unsubscribe from this group and stop receiving emails from it, send=20 > an email to std-proposals+unsubscribe@isocpp.org=20 > . > To post to this group, send email to std-proposals@isocpp.org=20 > . > To view this discussion on the web visit=20 > https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/3fbbd6b8-908= 7-4c02-bf66-632b7eff480d%40isocpp.org=20 > . --=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/7aa018bf-dcaa-6c95-dd64-413990592c37%40wanadoo.f= r. --------------D4F2F8D6BC7572938EFADC2F Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Le 05/02/2017 =C3=A0 14:22, Bengt Gustaf= sson a =C3=A9crit=C2=A0:
@Vicente: You present some nice solutions for the current language, but the drawback is of course that it is not obvious that it is forbidden=C2=A0to change the default valu= e of the parameter.
I don't understand, could you clarify?
The other, minor, issue is that the template parameter name is not usable outside the template itself, which the typedef name would be.
Yes, this could be important on the base class case. For this case you could define a nested alias.

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

Could you show an example where the base type is needed outside the Derived class?

Nevertheless it is of course advisable to mention theses possibilities in a future proposal, as you say.

I see a problem with the proposal in that it has fairly complicated rules to learn, and the meaning differs depending on where you place your public's and const's. I'm not sure if the utility of the function outweighs the extra burden of having to learn and remember these extra rules.
I agree with you here. It is too complex. We just need a name.

Vicente

We also have decltype to solve some of the use cases.


Den s=C3=B6ndag 5 februari 2017 kl. 13:56:12 UTC+1 skrev TONGARI = J:
On Sunday, February 5, 2017 at 6:41:36 PM UTC+8, Vicente J. Botet Escriba wrote:=C2=A0
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 <= span style=3D"color:#660">typename MetaFunc<blahblah...>::type ><= /span>
T f() // yay!
{
=C2=A0 =C2=A0 /= / Use `T` from now on...
}
In this case, it's just an alternative w/o (ab)using the template param, like how concept-lite tries to eliminate enable_if trick.
=C2=A0
template<blahblah..., typename Base=3D= typename MetaFunc<blahblah...>::type>
class Derived : public Base // yay!
{
=C2=A0 =C2=A0 /= / Use `Base` from now on...
}
=C2=A0
This does not work if "blahblah...", is actually a template parameter pack, which has to be the last one.
In parameter list:
template<blahblah...>
void f(typedef SomeTemplate<blahblah...> T a, T b); // yay!

I'm not sure the = blahblah could be inferred

Do tou mean


template<class U>
void f(U, typedef SomeTemplate<U> T a, T b);

I mean something like:
template<class... Args>
void f(typedef std::tuple<Args...> T a, T b);

f(std::make_tuple(1, 2), std::make_tuple(= 3, 4)); //Args =3D=3D {int, int}, T =3D= =3D std::tuple<int, int>
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