220 38143 <1bc6ebbe-4d52-40b7-9e06-d096e76631ba@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Raymund Hofmann Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Better DRY when initializing members in constructor Date: Mon, 21 May 2018 00:23:18 -0700 (PDT) Lines: 120 Approved: news@gmane.org Message-ID: <1bc6ebbe-4d52-40b7-9e06-d096e76631ba@isocpp.org> References: <20180521070748.GA3811@noemi.bahnhof.se> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_26791_883090159.1526887398883" X-Trace: blaine.gmane.org 1526887274 24584 195.159.176.226 (21 May 2018 07:21:14 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 21 May 2018 07:21:14 +0000 (UTC) Cc: hofmannraymund@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCHZVUUFSEJRBZ7HRHMAKGQERUPC73Y@isocpp.org Mon May 21 09:21:10 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qk0-f200.google.com ([209.85.220.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fKf81-0006HR-DW for gclcip-std-proposals@m.gmane.org; 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Mon, 21 May 2018 00:23:20 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:ac8:22d7:: with SMTP id g23-v6ls6817304qta.10.gmail; Mon, 21 May 2018 00:23:19 -0700 (PDT) X-Received: by 2002:ac8:7293:: with SMTP id v19-v6mr1327985qto.0.1526887399306; Mon, 21 May 2018 00:23:19 -0700 (PDT) In-Reply-To: <20180521070748.GA3811@noemi.bahnhof.se> X-Original-Sender: hofmannraymund@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:38143 Archived-At: ------=_Part_26791_883090159.1526887398883 Content-Type: multipart/alternative; boundary="----=_Part_26792_1421355074.1526887398883" ------=_Part_26792_1421355074.1526887398883 Content-Type: text/plain; charset="UTF-8" I am aware of that, In my example you can see i already used what you propose in a slightly more indirect way, because it has limitations: struct T { struct I { int i; const char* cp; } m; T(const I& i) : m(i) {} }; usage: void testf() { T t({ 1,"abc" }); } I chose this way because if you inherit for example from std:: enable_shared_from_this, you lose the ability to initialize members in the way you have shown, you are required to have a constructor then: struct TS : std::enable_shared_from_this { struct I { int i; const char* cp; } m; //TS(const I& i) : m(i) {} }; TS ts{ 1,"abc" }; // error even worse, when you create a object with make_shared like so: struct TS : std::enable_shared_from_this { struct I { int i; const char* cp; } m; TS(const I& i) : m(i) {} }; void testf() { auto so = std::make_shared(TS::I{ 1,"abc" }); } You have to repeat I defined in TS, or alternatively write a constructor which needs too much repetition as mentioned. -- 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/1bc6ebbe-4d52-40b7-9e06-d096e76631ba%40isocpp.org. ------=_Part_26792_1421355074.1526887398883 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
I am aware= of that, In my example you can see i already used what you propose in a sl= ightly more indirect way, because it has limitations:

struct T=
{
=C2=A0=C2=A0=C2=A0 struct I
=C2=A0=C2=A0=C2=A0 {
=C2=A0=C2= =A0=C2=A0 =C2=A0=C2=A0=C2=A0 int i;
=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2= =A0 const char* cp;
=C2=A0=C2=A0=C2=A0 } m;
=C2=A0=C2=A0=C2=A0 T(cons= t I& i) : m(i) {}
};

usage:

void testf()<= br>{
=C2=A0=C2=A0=C2=A0 T t({ 1,"abc" });
}

I chose = this way because if you inherit for example from std::enable_shared_from_this, y= ou lose the ability to initialize members in the way you have shown, you ar= e required to have a constructor then:

struct TS : std::enable_share= d_from_this<T>
{
=C2=A0=C2=A0=C2=A0 struct I
=C2=A0=C2=A0=C2= =A0 {
=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 int i;
=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0 const char* cp;
=C2=A0=C2=A0=C2=A0 } m;
=C2=A0=C2= =A0=C2=A0 //TS(const I& i) : m(i) {}
};

TS ts{ 1,"abc&qu= ot; }; // error

even worse, when you create a object with make_share= d like so:

struct TS : std::enable_shared_from_this<T>
{=C2=A0=C2=A0=C2=A0 struct I
=C2=A0=C2=A0=C2=A0 {
=C2=A0=C2=A0=C2=A0 = =C2=A0=C2=A0=C2=A0 int i;
=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 const ch= ar* cp;
=C2=A0=C2=A0=C2=A0 } m;
=C2=A0=C2=A0=C2=A0 TS(const I& i)= : m(i) {}
};

void testf()
{
=C2=A0=C2=A0=C2=A0 auto so =3D= std::make_shared<T>(TS::I{ 1,"abc" });
}

You hav= e to repeat I defined in TS, or alternatively write a constructor which nee= ds too much repetition as mentioned.


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