220 32338 article Path: news.gmane.org!.POSTED!not-for-mail From: Tony V E Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: =?UTF-8?B?UmU6IFtzdGQtcHJvcG9zYWxzXSBSZTogQWRkaW5nIHRoZSBLZXl3b3JkIOKAnGludGVyZg==?= =?UTF-8?B?YWNl4oCdIGluIEMrKw==?= Date: Mon, 8 May 2017 16:11:35 -0400 Lines: 190 Approved: news@gmane.org Message-ID: 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/alternative; boundary=f403045f2ed6a0c634054f08d81f X-Trace: blaine.gmane.org 1494274297 31023 195.159.176.226 (8 May 2017 20:11:37 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 8 May 2017 20:11:37 +0000 (UTC) To: Standard Proposals Original-X-From: std-proposals+bncBCUZ5QWKNQIPTIODZACRUBHGXK7XI@isocpp.org Mon May 08 22:11:33 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f71.google.com ([74.125.82.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1d7p0H-0007yT-42 for gclcip-std-proposals@m.gmane.org; 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[2a00:1450:400c:c0c::229]) by mx.google.com with ESMTPS id v102si16202463wrb.15.2017.05.08.13.11.36 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 08 May 2017 13:11:36 -0700 (PDT) Received-SPF: pass (google.com: domain of tvaneerd@gmail.com designates 2a00:1450:400c:c0c::229 as permitted sender) client-ip=2a00:1450:400c:c0c::229; Original-Received: by mail-wr0-x229.google.com with SMTP id l9so53547560wre.1 for ; Mon, 08 May 2017 13:11:36 -0700 (PDT) X-Received: by 10.223.161.194 with SMTP id v2mr42128951wrv.132.1494274296299; Mon, 08 May 2017 13:11:36 -0700 (PDT) Original-Received: by 10.28.232.24 with HTTP; Mon, 8 May 2017 13:11:35 -0700 (PDT) In-Reply-To: X-Original-Sender: tvaneerd@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of tvaneerd@gmail.com designates 2a00:1450:400c:c0c::229 as permitted sender) smtp.mailfrom=tvaneerd@gmail.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=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:32338 Archived-At: --f403045f2ed6a0c634054f08d81f Content-Type: text/plain; charset="UTF-8" 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 > > The concept it matches is defined by the set of member functions in the > `interface`. The `interface` class will automatically generate matching > member functions which forward calls to the type-erased pointer/reference. > > So it's not a "virtual" call in the language sense; it's a virtual call in > the polymorphic sense. > > I like the idea of being able to take a concept and turn it into a type > that can type-erase any type that matches the concept. This allows you to > turn a compile-time polymorphism tool into a runtime polymorphism tool. But > if you want to do it directly through concepts, then this should include > more than just member functions. The type-erasure/code generation now needs > to include any operations specified by the concept, including overloaded > operators, global ADL functions, and the like. > > I would also want to see some way of defining copy/move behavior. That is, > whether the conversion to the "interface" type will create its own object > (like `any` or `function`) or whether it will just reference an existing > one, as well as specifying whether the type is move-only or copyable. > > -- > 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/e8fb03f4-8c94-46c2- > a612-acab81117998%40isocpp.org > > . > -- Be seeing you, Tony -- 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/CAOHCbiswurpbE6tG3igWTsFfpJ%3DLAeT9PoTUZBNsrnMOhEwSxQ%40mail.gmail.com. --f403045f2ed6a0c634054f08d81f Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Mon, May 8, 2017 at 11:16 AM, Nicol Bolas <jmckesson@gmail.com> wrote:
On Monday, May 8, 2017 at 10:54:13 AM UTC-4, Thiago Macieira w= rote:
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
=C2=A0

The concept it matches is defined by the set= of member functions in the `interface`. The `interface` class will automat= ically generate matching member functions which forward calls to the type-e= rased pointer/reference.

So it's not a "virtual" call = in the language sense; it's a virtual call in the polymorphic sense.
I like the idea of being able to take a concept and turn it into a typ= e that can type-erase any type that matches the concept. This allows you to= turn a compile-time polymorphism tool into a runtime polymorphism tool. Bu= t if you want to do it directly through concepts, then this should include = more than just member functions. The type-erasure/code generation now needs= to include any operations specified by the concept, including overloaded o= perators, global ADL functions, and the like.

I would also want to s= ee some way of defining copy/move behavior. That is, whether the conversion= to the "interface" type will create its own object (like `any` o= r `function`) or whether it will just reference an existing one, as well as= specifying whether the type is move-only or copyable.

--
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-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/e8fb= 03f4-8c94-46c2-a612-acab81117998%40isocpp.org.



--
Be seeing = you,
Tony

--
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To view this discussion on the web visit h= ttps://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAOHCbiswurpbE6= tG3igWTsFfpJ%3DLAeT9PoTUZBNsrnMOhEwSxQ%40mail.gmail.com.
--f403045f2ed6a0c634054f08d81f-- .