220 30777 <3fbbd6b8-9087-4c02-bf66-632b7eff480d@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Bengt Gustafsson Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Make Typedef Great Again Date: Sun, 5 Feb 2017 05:22:36 -0800 (PST) Lines: 269 Approved: news@gmane.org Message-ID: <3fbbd6b8-9087-4c02-bf66-632b7eff480d@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1026_1088320546.1486300956941" X-Trace: blaine.gmane.org 1486300959 6047 195.159.176.226 (5 Feb 2017 13:22:39 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 5 Feb 2017 13:22:39 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCRIRSPDTQIRBHOO3TCAKGQENXGBJKA@isocpp.org Sun Feb 05 14:22:34 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pf0-f199.google.com ([209.85.192.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1caMm1-0001Hg-8V for gclcip-std-proposals@m.gmane.org; Sun, 05 Feb 2017 14:22:33 +0100 Original-Received: by mail-pf0-f199.google.com with SMTP id y143sf78935017pfb.6 for ; Sun, 05 Feb 2017 05:22:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=pzKzSepzXcNVLWd31irdsHvIsxU5Sx8IIA8fAif5swA=; b=HCRFb00PHroYp9jG9eBaan61DUpiUtFP8kRv3zMeMlgMBVc/yCFjzrhFMtJCSl3c2V Q12Utp1gJSTRuVMkKcyZaOGwxKsEDAOGj9XRPGGdm0aPrZ9nmUZLqbpluvXVlTmj+cHA /GjOVvpKpVB2k87HbFFz819qph4n3d78K2t5KZAdn8cZMfaenZ5+uiCqcH8CwcfhheUV ZXSV3+0eZWWtZOZqcAb51B5zaMei8u8sx3X4oY+JtTucz7ss6M2LWeERHNsgzDw3P7Ym Of+OPs1F7O09DXUb4X58JHBalvVnCkQwFo2s20earVZvkatk29I8nLwmfkCi7JAh35Df qOKQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:x-original-sender:reply-to:precedence :mailing-list:list-id:x-spam-checked-in-group:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=pzKzSepzXcNVLWd31irdsHvIsxU5Sx8IIA8fAif5swA=; b=qiAtRhjp87SlB1Z7+NusatAGVIThFnARhhA5dOFtMsJOFxfY2RCd32mdU1BuPIytq8 BOq+FgdssxC7+ejIPZcI/WvMWElGspbk+bRtCjzXAhUofB9YP3Nnz2KhSMdn83Z9S8MC Zu0S/jnC08PcisJNz+2s+MCgPolE38HdxJEB/ei665ZnzrUJN5mWCa5ucmeFtsKX8U7x P86qYFUhi2LktKcE7n8MEMbQeOYdsuLYoErfYO2/OprKYK/6Ot0XA/hPXGro/pfeA+ei gsRHucg4xmnZxAENRW3AeuP6aSkqogPcn9Vi+XgsyjUyLSa8Tzp2HjK3cjJ3nHIrGZlc sKXw== X-Gm-Message-State: AIkVDXL2cU8mtyBqRnjUzCmY6eDFCgj5HHUMrw4AvxA2DucsXLoRF1950+SC6EIHLvH60Q== X-Received: by 10.99.132.195 with SMTP id k186mr1474153pgd.147.1486300958488; Sun, 05 Feb 2017 05:22:38 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.0.1 with SMTP id 1ls11525196ota.5.gmail; Sun, 05 Feb 2017 05:22:37 -0800 (PST) X-Received: by 10.157.18.211 with SMTP id g77mr320670otg.14.1486300957457; Sun, 05 Feb 2017 05:22:37 -0800 (PST) In-Reply-To: X-Original-Sender: bengt.gustafsson@beamways.com 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:30777 Archived-At: ------=_Part_1026_1088320546.1486300956941 Content-Type: multipart/alternative; boundary="----=_Part_1027_635710659.1486300956942" ------=_Part_1027_635710659.1486300956942 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable @Vicente: You present some nice solutions for the current language, but the= =20 drawback is of course that it is not obvious that it is *forbidden* to=20 change the default value of the parameter. The other, minor, issue is that= =20 the template parameter name is not usable outside the template itself,=20 which the typedef name would be. Nevertheless it is of course advisable to mention theses possibilities in a= =20 future proposal, as you say. I see a problem with the proposal in that it has fairly complicated rules= =20 to learn, and the meaning differs depending on where you place your=20 public's and const's. I'm not sure if the utility of the function outweighs= =20 the extra burden of having to learn and remember these extra rules. 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= =20 > wrote:=20 >> >> 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::typ= e > >> T f() // yay! >> { >> // Use `T` from now on... >> } >> >> In this case, it's just an alternative w/o (ab)using the template param,= =20 > like how concept-lite tries to eliminate enable_if trick. > =20 > >> template::ty= pe> >> class Derived : public Base // yay! >> { >> // Use `Base` from now on... >> } >> > =20 > This does not work if "blahblah...", is actually a template parameter=20 > pack, which has to be the last one. > >> In parameter list: >> template >> void f(typedef SomeTemplate T a, T b); // yay! >> >> I'm not sure the blahblah could be inferred >> >> Do tou mean >> >> >> template >> void f(U, typedef SomeTemplate T a, T b); >> > > I mean something like: > template > void f(typedef std::tuple T a, T b); > > f(std::make_tuple(1, 2), std::make_tuple(3, 4)); //Args =3D=3D {int, int}= , T=20 > =3D=3D std::tuple > --=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/3fbbd6b8-9087-4c02-bf66-632b7eff480d%40isocpp.or= g. ------=_Part_1027_635710659.1486300956942 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
@Vicente: You present some nice solutions for the current = language, but the drawback is of course that it is not obvious that it is <= i>forbidden=C2=A0to change the default value of the parameter. The othe= r, minor, issue is that the template parameter name is not usable outside t= he template itself, which the typedef name would be.

Nev= ertheless it is of course advisable to mention theses possibilities in a fu= ture proposal, as you say.

I see a problem with th= e proposal in that it has fairly complicated rules to learn, and the meanin= g 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 o= f having to learn and remember these extra rules.

= 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, 2= 017 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 typename MetaFunc<blahblah= ...>::type = >
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 co= ncept-lite tries to eliminate enable_if trick.
=C2=A0
template<blahblah..., typename Base=3Dtypename MetaFunc<blahblah...>::type= >
class Derived : pu= blic Base // yay!
{
=C2=A0 =C2=A0 // Use `Base` f= rom now on...
}
=C2=A0
This does not work if "blahblah...", is actually a template parameter pack, which = has to be the last one.
=20
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&= gt;

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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/3fbbd6b8-9087-4c02-bf66-632b7eff480d= %40isocpp.org.
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