220 10426 <2be92780-bf68-4634-a193-7461f71de3f7@isocpp.org> article Path: news.gmane.org!not-for-mail From: douglas.boffey@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Generated initializer_list Date: Tue, 29 Apr 2014 02:53:34 -0700 (PDT) Lines: 141 Approved: news@gmane.org Message-ID: <2be92780-bf68-4634-a193-7461f71de3f7@isocpp.org> References: <357dd72f-c749-4dc5-aa6d-5ac4528aba5a@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_638_15144896.1398765214779" X-Trace: ger.gmane.org 1398765225 26225 80.91.229.3 (29 Apr 2014 09:53:45 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 29 Apr 2014 09:53:45 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDSIZVXVVUFBBH7N7WNAKGQECHXFE4A@isocpp.org Tue Apr 29 11:53:39 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qc0-f198.google.com ([209.85.216.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Wf4jL-0005uU-2N for gclcip-std-proposals@m.gmane.org; Tue, 29 Apr 2014 11:53:39 +0200 Original-Received: by mail-qc0-f198.google.com with SMTP id r5sf28433956qcx.9 for ; Tue, 29 Apr 2014 02:53:36 -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 :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe :content-type; bh=PzcB6Mdxr3pN5/FlAoBLR30IIP82hkIExp/Z32kvago=; b=ve1raWAtTlPOSqvZ9AxleN0zKDfLNEQXzrMaI7lI/gaYt+MFfH7y/GTh6kMrS1+C/U tl/0YjJ7ojcacJ2WjFbVcZ+L9IACuhli24Kq/ufFTQCwjT5CLur8vOMxLmlkxzixAyUc ciQ3Ejzg64U49L8ir4hBBsHHXqQZ1ckCq3vGLt+eYcjy8sLYSJbNYb4FiEXFXZ+hFB/Y GXEZAjAxN9kRGh7K9DmYtwNtlA1gyTRtpZfVn38OTSWfOFbozu0rq9wuLcUcgi9OteSo AARbvwxPgB9m8CBwzqGLdpYnQi3U96RdHr10GJILAag4kxXHhsPUIvTpZUYJ8CqkXk4M Enew== 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:x-original-sender:reply-to:precedence :mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=PzcB6Mdxr3pN5/FlAoBLR30IIP82hkIExp/Z32kvago=; b=BOI+kLKcBuSeYSHV0n0LjGhT8CbtFwtqCexti1tVRpC/N1OyjUIie9yM9Fivv5fHki 73C7tfWFerxozXBA3ZwlLunbWL3iy34OWm3mS2GuvZOiDZAkTs0uZSZqllZxysrB+/s2 1Z341DjirtHyFNehhUF0xpPRXOl/HOGq5i5EGt3qTdSRaJxgOwWNor3LxK+/USkqw7/T 29VyiYz7E/hBX//yARFHP8gwzRiN0M+qvfTt6CHRSIZ8kHt6tAauOaHBcpCQ8dyKHRpI pMZkvrSbQ3JqMhph2v81tsClmyGrWSINXUcZzGWeHHVr3TK0fvV+VSL1NlCdPM4MrXQQ zHPQ== X-Gm-Message-State: ALoCoQnCyO6fxIYAUFTug+CZ1sNb/v1ex+hB5Ox3x4ZY9IkH+BsgC6PJ+wn1Wfs/GSre8KI81ovZ X-Received: by 10.236.231.52 with SMTP id k50mr13912579yhq.52.1398765216267; Tue, 29 Apr 2014 02:53:36 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.80.145 with SMTP id c17ls27535qgd.60.gmail; Tue, 29 Apr 2014 02:53:35 -0700 (PDT) X-Received: by 10.140.104.168 with SMTP id a37mr17786qgf.20.1398765215541; Tue, 29 Apr 2014 02:53:35 -0700 (PDT) In-Reply-To: X-Original-Sender: douglasboffey@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:10426 Archived-At: ------=_Part_638_15144896.1398765214779 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable > > To represent a compile-time sequence of values of a given literal type=20 >> T you can use an array defined with constexpr:=20 >> >> constexpr T a[] =3D ...;=20 >> > The problem with that is that the array is a list of literals=20 (or constexprs). There should be a method to generate the list from an=20 algorithm, and have the generated list stored in the object file. As far= =20 as I can tell, that facility is not available, either in core, nor in the= =20 library. I would like to type something along the lines of: =20 constexpr auto primes[5] =3D get_nth_prime; =20 given a function =20 constexpr unsigned int get_nth_prime(size_t n) =20 which would be equivalent to =20 constexpr unsigned int primes[] =3D {2, 3, 5, 7, 11}; =20 > If the values differ in type you can use a class type of literal type:=20 >> >> constexpr struct=20 >> {=20 >> T1 v1;=20 >> T2 v2;=20 >> T3 v3;=20 >> } S =3D ...;=20 >> >> There are a few other options, but it isn't clear from your example=20 >> what the problem is with the above. In all cases you can write a=20 >> constexpr function that returns the above types (well, you need to=20 >> wrap the array in a struct to return it as usual). You can create a=20 >> mutable local variable of the type within the constexpr function, fill= =20 >> it out, and return it:=20 >> >> There are some limitations on literal types that different people are=20 >> thinking about and working on, but it isn't clear which one (if any)=20 >> you are hitting upon.=20 > > > This again misses the point=E2=80=94I=E2=80=99m not talking about aggrega= tes of different=20 types. I am sorry if my example was not clear. > =20 --=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_638_15144896.1398765214779 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
To represent a compile-time sequen= ce of values of a given literal type
T you can use an array defined wit= h constexpr:

    constexpr T a[] =3D ...;
The problem with that is that the array is a list of literals (or = ;constexprs).  There should be a method to generate the list from an a= lgorithm, and have the generated list stored in the object file.  As f= ar as I can tell, that facility is not available, either in core, nor in th= e library.
I would like to type something along the lines of:
 
constexpr auto primes[5] =3D get_nth_prime;
 
given a function
 
constexpr unsigned int get_nth_prime(size_t= n)
 
which would be equivalent to
 
constexpr unsigned int primes[] =3D {2= , 3, 5, 7, 11};
 
If the values differ in type you c= an use a class type of literal type:

    constexpr struct=
    {
         T1 v1;
 = ;        T2 v2;
         T= 3 v3;
    } S =3D ...;

There are a few other options,= but it isn't clear from your example
what the problem is with the abov= e.  In all cases you can write a
constexpr function that returns t= he above types (well, you need to
wrap the array in a struct to return = it as usual).  You can create a
mutable local variable of the type= within the constexpr function, fill
it out, and return it:

The= re are some limitations on literal types that different people are
thin= king about and working on, but it isn't clear which one (if any)
you ar= e hitting upon.

This again misses the point=E2=80=94I=E2=80=99m not talking about aggr= egates of different types.  I am sorry if my example was not clear.
 

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