220 32339 <6bfa8a30-a2c4-46d5-8ac2-c0353408a041@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: =?UTF-8?B?UmU6IFtzdGQtcHJvcG9zYWxzXSBSZTogQWRkaW5nIHRoZSBLZXl3b3JkIOKAnGludGVyZg==?= =?UTF-8?B?YWNl4oCdIGluIEMrKw==?= Date: Mon, 8 May 2017 13:44:58 -0700 (PDT) Lines: 143 Approved: news@gmane.org Message-ID: <6bfa8a30-a2c4-46d5-8ac2-c0353408a041@isocpp.org> References: <9ee212eb-4037-40c4-94c3-57a9a170a4c3@isocpp.org> <1765502.4y06pMOS3s@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_4619_1861128834.1494276299009" X-Trace: blaine.gmane.org 1494276303 9931 195.159.176.226 (8 May 2017 20:45:03 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 8 May 2017 20:45:03 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBS5RYPEAKGQE7EXML7I@isocpp.org Mon May 08 22:44:59 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qt0-f197.google.com ([209.85.216.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1d7pWZ-0002NW-U2 for gclcip-std-proposals@m.gmane.org; Mon, 08 May 2017 22:44:56 +0200 Original-Received: by mail-qt0-f197.google.com with SMTP id n4sf33270418qte.3 for ; Mon, 08 May 2017 13:45:01 -0700 (PDT) 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=Hxxkx2WdpPHhutbUQwmRKEmpbeJCSW/8657UHAE6a6Y=; b=m++V0ge4VSlVURNUPXIUBilBJVIhLRM3j27ss98JbcARg9WXn1i3i/HHFPrj4IJJNa mpilhwLX+TuC0KhPvYg5hOzTtSxEbKhTD/Lqez4qqHY23S28+7MpTlLQK7/iVALri6Rf 6QyK4GcdBo+K66VGyOVavTSc7qU24MWROdzN7ra48fpW3QBEoBj3Gk/NN+EvtG0CCHg3 1HG98g46DypJZ1cBqbahE5D47OZHYa+U02Jkx/0gXSKgK24uQDk2WSmstqf+ssM64wwX ONCcnuX1fFC2LZ1n03k7VIhr4o27iRV/hMs4hV0NT0qwdj25+kKUjJJsIJZuagbjkNoq 1Huw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; 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=Hxxkx2WdpPHhutbUQwmRKEmpbeJCSW/8657UHAE6a6Y=; b=h7C1+yZsgBn3pvVnFkggkKc9o6J/u8rK5GaWnKy3HKwAuVdQCVHGk9i3UFdCVaRQws fQrax3o/E6vuX+T9bH6910l/kCk0YPBBCQLf12vlnHX7rDi/caoDdHNzUaps4s5oeUVf 0bOUzl7W42fHXx5M33focOunaA6v9Lwl+5ssO6/liiOe9lz8jnbEPSuBvfWlQuoP6DA2 Pcn2ePLB/iiA+s24GdsxURaracoD/I3etertP8Wef7QVTA2KoRvS40hH2OHsXuZtjM6+ 8xfe8XSn+Xm9bOwaKMwo2+vZRgfFmattw7ljAZ23mpasaOuJbdK5AX5xhKu0KG6ck7EZ vGEg== 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=Hxxkx2WdpPHhutbUQwmRKEmpbeJCSW/8657UHAE6a6Y=; b=AA37kW3p+3Lsvxna/sp5VfocOjP2JfqoVeQv5e+7AsyTX4HhiB1uUSCp1DlvrXP5fR A8A9hYiZrwzl5w5izzOWvHYv1RC64Ab2pn8DJ8zXvRMKnNpImm2G/xjTDvCkec0TRLeL 8WF7kmQiCPI8bwS6gP9h2ZugLztc7EnRL/DqVss5RI8v3yFa+0LwyVN5SttSlCjm42m0 Z/OvJS9Y11blosdsfMG5rrEGzBxKdh/drQhpHEIffdMUuuTqGWsKokmOt7zYPGCZOOry DPNPdSAwwc9PoHJqfhl8hn7COhuICZcdQb6dgJ3MtNDwy6aumJX84pGFnbJl8zFU62bH ioAw== X-Gm-Message-State: AN3rC/6SSXzvaTgwWHc8FnH3nkIUvGMx8P7VngXcx+92MwwtAPnVjbNJ 9bqgjs51ue7wQw== X-Received: by 10.200.33.215 with SMTP id 23mr28887571qtz.29.1494276300503; Mon, 08 May 2017 13:45:00 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.89.238 with SMTP id u46ls10060546otg.2.gmail; Mon, 08 May 2017 13:44:59 -0700 (PDT) X-Received: by 10.157.55.133 with SMTP id x5mr822746otb.10.1494276299559; Mon, 08 May 2017 13:44:59 -0700 (PDT) In-Reply-To: X-Original-Sender: jmckesson@gmail.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:32339 Archived-At: ------=_Part_4619_1861128834.1494276299009 Content-Type: multipart/alternative; boundary="----=_Part_4620_753737676.1494276299009" ------=_Part_4620_753737676.1494276299009 Content-Type: text/plain; charset=UTF-8 On Monday, May 8, 2017 at 4:11:38 PM UTC-4, Tony V E wrote: > > On Mon, May 8, 2017 at 11:16 AM, Nicol Bolas > wrote: > >> On Monday, May 8, 2017 at 10:54:13 AM UTC-4, Thiago Macieira wrote: >>> >>> On Monday, 8 May 2017 00:30:58 PDT Mingxin Wang wrote: >>> > Unlike the "*Concespts*" that work at compile time, the >>> > "*Interfaces*" work at runtime mostly. In essence, it is not only >>> > a syntactic sugar, but a style of implementation for *polymorphism*: >>> > virtual functions are only generated when required at runtime >>> >>> "virtual functions generated at runtime" needs A LOT of explanation. >>> Please >>> explain how the compiler would implement such a thing. >>> >>> i also recommend finding another name for your feature. "interface" is a >>> widely >>> known term and means something else: it means a base class with virtuals >>> that >>> need to be overridden. >>> >> >> I think the idea that he's trying to get across is the following. >> >> An `interface` is a class which is implicitly convertible from any type >> which matches some concept. The implicit conversion effectively works by >> storing a type-erased pointer/reference to the object it is converted from. >> > > > Yep, I think we are talking about automatic type-erasure here. > > Sean Parent has done a lot of work with type-erasure and polymorphic > values types based on "concepts" (pre Concepts concepts). > > I wonder if Concepts + reflection might allow someone to write: > > Foo foo; // foo happens to model Concept > std::erased efoo = foo; > func(efoo); // Not a templatized function > > Tony > That would require lots of things that don't exist at present: 1: Reflection to be able to introspect concepts, being able to iterate over their constituent expressions. 2: Reflection would need to be able to *generate* code. Otherwise, `std::erased` wouldn't be able to generate non-member functions to handle non-members of the `Concept`. 3: Concepts would have to be able to be passed as template parameters. -- 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 email 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/6bfa8a30-a2c4-46d5-8ac2-c0353408a041%40isocpp.org. ------=_Part_4620_753737676.1494276299009 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Monday, May 8, 2017 at 4:11:38 PM UTC-4, Tony V E wrote= :
On Mon, May 8, 2017 at 11:16 AM, Nicol Bolas <jmck...@gmail.com> wrote:
On Monday, May 8, 2017 at 10:54:13 AM UTC-4, = Thiago Macieira wrote:
On Monday, 8 = May 2017 00:30:58 PDT Mingxin Wang wrote:
> Unlike the "*Concespts*" that work at compile time, the
> "*Interfaces*" work at runtime mostly. In essence, it is= not only
> a syntactic sugar, but a style of implementation for *polymorphism= *:
> virtual functions are only generated when required at runtime

"virtual functions generated at runtime" needs A LOT of expla= nation. Please=20
explain how the compiler would implement such a thing.

i also recommend finding another name for your feature. "interface= " is a widely=20
known term and means something else: it means a base class with virtual= s that=20
need to be overridden.

I think the idea= that he's trying to get across is the following.

An `interface`= is a class which is implicitly convertible from any type which matches som= e concept. The implicit conversion effectively works by storing a type-eras= ed pointer/reference to the object it is converted from.


Yep, I think we are talking about automat= ic type-erasure here.

Sean Parent has done a lot of work = with type-erasure and polymorphic values types based on "concepts"= ; (pre Concepts concepts).

I wonder if Concepts + reflect= ion might allow someone to write:

Foo foo; // foo happens= to model Concept
std::erased<Concept> efoo =3D foo;
func(efoo);=C2=A0 // Not a templatized function
<= br>
Tony

That wo= uld require lots of things that don't exist at present:

1: Refle= ction to be able to introspect concepts, being able to iterate over their c= onstituent expressions.

2: Reflection would need to be able to ge= nerate code. Otherwise, `std::erased` wouldn't be able to generate = non-member functions to handle non-members of the `Concept`.

3: Conc= epts would have to be able to be passed as template parameters.

--
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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/6bfa8a30-a2c4-46d5-8ac2-c0353408a041= %40isocpp.org.
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