220 34709 <20171009040212.5161043.12800.37351@gmail.com> article Path: news.gmane.org!.POSTED!not-for-mail From: Tony V E Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Extensions for Disambiguation Tags Date: Mon, 09 Oct 2017 00:02:12 -0400 Lines: 106 Approved: news@gmane.org Message-ID: <20171009040212.5161043.12800.37351@gmail.com> References: <527c448b-b8dd-4877-b63f-b399c167da4d@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1507521743 25397 195.159.176.226 (9 Oct 2017 04:02:23 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 9 Oct 2017 04:02:23 +0000 (UTC) To: Mingxin Wang , ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCUZ5QWKNQIMN2PLZYCRUBCD7TVKE@isocpp.org Mon Oct 09 06:02:12 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f70.google.com ([209.85.218.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1e1PGa-0004kE-9V for gclcip-std-proposals@m.gmane.org; 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How about some examples showing usage?
= =

= = =
Sent from my BlackBer= ry portable Babbage Device
= = = =
From: Mingxin Wang=
Sent: Sunday, October 8, 2017 10:08 PM
To: <= /b>ISO C++ Standard - Future Proposals
Reply To: std-propo= sals@isocpp.org
Subject: [std-proposals] Extensions for Di= sambiguation Tags

I think the disambiguation tags defined in the standard are not en= ough to carry every sort of metadata required by function templates, and th= erefore I suggest the following two additional disambiguation tags:

= template <class T, T V>
struct in_= place_arg_t {
  explicit in_place_a= rg_t() =3D default;
};
template <class T, T V>
inline constexpr in_place_arg_t<T, V> in_place_arg {};

temp= late <class T, const T& V>
str= uct in_place_resource_t {
  explici= t in_place_resource_t() =3D default;
};<= /div>
template <class T, const T& V>=
inline constexpr in_place_resource_t<= ;T, V> in_place_resource {};

Use= rs are allowed to pass constexpr values by `in_place_arg`, and pass static = constexpr resources by `in_place_resource`.

Additi= onally, I suggest that `in_place_index_t` should be an alias of `in_place_a= rg_t`:

te= mplate <size_t I>
using in_place_i= ndex_t =3D in_place_arg_t<size_t, I>;

Moreover, comparing to `in_place_arg_t`, I think `integral_constant` is i= nappropriately named, and there seem to be little necessity to define any m= ember types or constants in it, because these metadata is already passed by= templates. This design is also considered as a solution to another thread = "Constexpr function parameters through special conversions<= /a>" started by Nicol Bolas.



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