220 20017 <0a8b46d3-4b38-4e1b-ad75-9d18b4697a97@isocpp.org> article Path: news.gmane.org!not-for-mail From: Sean Middleditch Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Obtaining the number of arguments of a function Date: Tue, 25 Aug 2015 16:21:52 -0700 (PDT) Lines: 123 Approved: news@gmane.org Message-ID: <0a8b46d3-4b38-4e1b-ad75-9d18b4697a97@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1668_1981265978.1440544912905" X-Trace: ger.gmane.org 1440544923 26133 80.91.229.3 (25 Aug 2015 23:22:03 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 25 Aug 2015 23:22:03 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCDODCNR2QPRBEXR6OXAKGQEMB4QAPI@isocpp.org Wed Aug 26 01:21:58 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f69.google.com ([209.85.213.69]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZUNXQ-0000Z3-T9 for gclcip-std-proposals@m.gmane.org; Wed, 26 Aug 2015 01:21:57 +0200 Original-Received: by vkd66 with SMTP id 66sf208866017vkd.3 for ; Tue, 25 Aug 2015 16:21:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :content-type: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=v3Fch86UAaXwvZrXOtJbpuxZYdLg3szk7acShFSC2YY=; b=E40PllSFw/ELPnbbaunvYnyX9tsb1plIixdrH0NfKFQwU+5/ZO0CTLIEnxeHkUJSOk ZNwvOcEneXNEE0rYO0CRc56EmFSTw9+FVgdgZANUtI21s3rIg+LL29cvbBHSsKuri5ZO XQg6ZQM6DtZCgdE9gC65Kns+ej9jtW8a3kHQyGqTtS26dZSZWoTf8MfLzTsS5K06BTKK H/sPASs+TyZfaFO/4U6Tph+hKQeeZ2dcR9fiPEH6wiMzr4XnfDrm9vlJ7ruwQcz96wUk WR4RdVKITQ5dbGpMff/Jh7u/RM9OBVjgwYTEYPXJLXBH9fqkOTLaIxMlGulRWfc19oUw 6ipw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:content-type: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=v3Fch86UAaXwvZrXOtJbpuxZYdLg3szk7acShFSC2YY=; b=QfiNUM+ZBE6brNa42Lmiqqv3YsSNeoMlb0LVBXiW9kCjSbQ/5TKpmuhPkqEnCIcxrw SLUD7m1Ci16eq74kZvTncdgQOjKB3cFGkL1vIotTuHyBif+q8nHdunicwpJcFf+qPVLG mfI6ZzzKBcaCN3dw3MIqzZCnEeQMidqjfbNnycj8N4AXLAYfAE3x51KWBapkSEOOyQS1 C3EqQoKD9MoK/kQLidneWO7p7ZuJHiZHKD5p8XxLax/kqUIBW+8BUL+8aRQs6B3nUIrV e10XhdgJdF6+rk6//uHljkjFXRZ+4H6mhhKqZCy8PdgtU7J0IVshPn3mv9iJgt0l5UTt ZRIw== X-Gm-Message-State: ALoCoQli3RQxrdfaVZ8Oauv7qt46MKh1YxzEM7DA2GlfVFbrOuF8bWspTbsHsmKHMR+65MrkGzof X-Received: by 10.129.159.69 with SMTP id w66mr4231303ywg.31.1440544916054; Tue, 25 Aug 2015 16:21:56 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.137.102 with SMTP id qh6ls304035igb.37.canary; Tue, 25 Aug 2015 16:21:54 -0700 (PDT) X-Received: by 10.50.138.70 with SMTP id qo6mr93647igb.13.1440544914252; Tue, 25 Aug 2015 16:21:54 -0700 (PDT) In-Reply-To: X-Original-Sender: Sean.Middleditch@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org 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:20017 Archived-At: ------=_Part_1668_1981265978.1440544912905 Content-Type: multipart/alternative; boundary="----=_Part_1669_424219494.1440544912906" ------=_Part_1669_424219494.1440544912906 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Sunday, August 23, 2015 at 1:34:09 AM UTC-7, David Krauss wrote: > > > On 2015=E2=80=9308=E2=80=9323, at 4:03 PM, NDos Dannyu >=20 > wrote: > > Why this function isn't in the stantard library? It's too easy to=20 > implement! > > > Is the standard library supposed to do everything that=E2=80=99s easy? > > *template * > *constexpr size_t count_args(R (*)(Args...)) noexcept {* > * return sizeof...(Args);* > *}* > > > This doesn=E2=80=99t handle member function signatures with cv-qualifiers= or=20 > ref-qualifiers. Separately, it doesn=E2=80=99t handle member functions (P= TMFs). It=20 > doesn=E2=80=99t handle C-style varargs signatures, or Callable objects be= sides=20 > function pointers. It doesn=E2=80=99t tell you about default arguments. > > This is *not* easy. I don=E2=80=99t see how it=E2=80=99s useful, either. > This is just one piece of boost function_traits=20 (http://www.boost.org/doc/libs/1_57_0/libs/type_traits/doc/html/boost_typet= raits/reference/function_traits.html)=20 combined with the utility to convert various forms of function pointer into= =20 the "function type" needed by function_traits=20 (e.g. https://functionalcpp.wordpress.com/2013/08/05/function-traits/) Very useful for script binding and general runtime reflection systems,=20 among other things. Take a look at libraries like luabind or one of its=20 umpteen bazillion alternatives for examples of where it can be useful. Suuuper common need in games at the very least, and I'm sure many other=20 places. Would be nice to have function_traits in the standard. --=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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. ------=_Part_1669_424219494.1440544912906 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Sunday, August 23, 2015 at 1:34:09 AM UTC-7, David Krauss wrote:
On 2015=E2=80=9308=E2=80=9323, at 4:0= 3 PM, NDos Dannyu <ndosp...@naver.com> wrote:

Why this function isn't in the stantard library? It's= too easy to implement!

I= s the standard library supposed to do everything that=E2=80=99s easy?
=
template &= lt;class R, class ...Args>
constexpr size_t c= ount_args(R (*)(Args...)) noexcept {
=C2=A0=C2= =A0=C2=A0 return sizeof...(Args);
}

This doesn=E2=80=99t handle membe= r function signatures with cv-qualifiers or ref-qualifiers. Separately, it = doesn=E2=80=99t handle member functions (PTMFs). It doesn=E2=80=99t handle = C-style varargs signatures, or Callable objects besides function pointers. = It doesn=E2=80=99t tell you about default arguments.

This is not=C2=A0easy. I don=E2=80=99t see how it=E2=80=99s usefu= l, either.

This is just one pie= ce of boost function_traits (http://www.boost.org/doc/libs/1_57_0/libs/type= _traits/doc/html/boost_typetraits/reference/function_traits.html) combined = with the utility to convert various forms of function pointer into the &quo= t;function type" needed by function_traits (e.g.=C2=A0https://function= alcpp.wordpress.com/2013/08/05/function-traits/)

V= ery useful for script binding and general runtime reflection systems, among= other things. Take a look at libraries like luabind or one of its umpteen = bazillion alternatives for examples of where it can be useful.
Suuuper common need in games at the very least, and I'm su= re many other places.

Would be nice to have fu= nction_traits in the standard.

--

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