220 22792 article Path: news.gmane.org!not-for-mail From: Andrew Tomazos Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Designated initializer list status? 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[2a00:1450:400c:c09::22b]) by mx.google.com with ESMTPS id f2si6955393wma.46.2015.11.21.07.22.34 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 21 Nov 2015 07:22:34 -0800 (PST) Received-SPF: pass (google.com: domain of andrewtomazos@gmail.com designates 2a00:1450:400c:c09::22b as permitted sender) client-ip=2a00:1450:400c:c09::22b; Original-Received: by wmww144 with SMTP id w144so54838160wmw.0 for ; Sat, 21 Nov 2015 07:22:34 -0800 (PST) X-Received: by 10.28.194.84 with SMTP id s81mr8379697wmf.51.1448119354764; Sat, 21 Nov 2015 07:22:34 -0800 (PST) Original-Received: by 10.28.223.69 with HTTP; Sat, 21 Nov 2015 07:22:34 -0800 (PST) In-Reply-To: <8b5cda67-8c22-41b6-b99d-ac2ab22f30d2@isocpp.org> X-Original-Sender: andrewtomazos@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of andrewtomazos@gmail.com designates 2a00:1450:400c:c09::22b as permitted sender) smtp.mailfrom=andrewtomazos@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=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-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:22792 Archived-At: --001a1148e93ebbb6d705250e8fdb Content-Type: text/plain; charset=UTF-8 https://groups.google.com/a/isocpp.org/forum/#!topic/std-proposals/IgDFqKjKlRs On Sat, Nov 21, 2015 at 3:11 PM, wrote: > Coming from Golang and C I was saddened by the fact that standard C++ > lacks (JSON-esque) designated initializer list support. > > Some pragmatic reasons to support it: > 1. It seem to be some interest in this feature, e.g. 33 votes: > http://stackoverflow.com/questions/18731707 > 2. It's makes C++ more compatible with C99. > 3. Many compilers already seem have support for it. I realized it wasn't > in C++ when I turned on --pedantic. > > A contrived example: > > // ... > > class Link { > public: > int bw; > Coord wr_c; > Coord bl_c; > int src; > int mtime; > Computer* dst; > int u; > }; > > // ... > > int main() { > // ... > std::vector links(m); > for (int i = 0; i < m; i++) { > int a, b, c; > std::cin >> a >> b >> c; > links[i] = {c, Coord(), Coord(), a, 0, &comps[b]}; // > Non-designated > links[i] = {.src = a, .dst = &comps[b], .bw = c}; // > Designated > } > // ... > } > > Some (likely highly subjective) problems with the non-designated syntax: > 1. Order dependent (harder to read). > 2. Does not scale well, parameter ordering is increasingly difficult to > track when more fields are added. > 3. Does not allow explicit initialization of a partial set of fields. > (harder to read, annoying to write) > > 1, 2: Understanding the designated initializer list assignment requires no > declaration or parameter order knowledge so the grammar is more context > free and therefore easier to read. > > 3: You are forced to write an explicit constructor or enumerate defaults > for all fields. An explicit constructor would require extra boilerplate and > introduce another independent order you have to track (more context). > Writing a constructor for a specific way you want to initialize a class > seems like code smell. > > So I hope this feature would become standardized. Thank you for reading > my humble opinion. > > -- > > --- > 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. > Visit this group at > http://groups.google.com/a/isocpp.org/group/std-proposals/. > -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. --001a1148e93ebbb6d705250e8fdb Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

On Sat, Nov 21, 2015 at 3:11 PM, <land= eholm@gmail.com> wrote:
Coming from Golang and C I was saddened by the fact that= standard C++ lacks (JSON-esque) designated initializer list support.

Some pragmatic reasons to support it:
1. = It seem to be some interest in this feature, e.g. 33 votes:=C2=A0http://stac= koverflow.com/questions/18731707
2. It's makes C++ more c= ompatible with C99.
3. Many compilers already seem have support f= or it. I realized it wasn't in C++ when I turned on --pedantic.

A contrived example:

=C2=A0 =C2=A0 // ...

=C2=A0 =C2=A0 class Link {
=C2=A0 =C2=A0 public:
=C2=A0 =C2=A0 =C2=A0 =C2=A0 int bw;
=C2=A0 =C2=A0 =C2=A0 =C2=A0 Coo= rd wr_c;
=C2=A0 =C2= =A0 =C2=A0 =C2=A0 Coord bl_c;
=C2=A0 =C2=A0 =C2=A0 =C2=A0 int src;
=C2=A0 =C2=A0 =C2=A0 =C2=A0 int mtime;
=C2=A0 =C2=A0 =C2=A0 =C2=A0 = Computer* dst;
=C2= =A0 =C2=A0 =C2=A0 =C2=A0 int u;
=C2=A0 =C2=A0 };

=C2=A0= =C2=A0 // ...

<= /font>
=C2=A0 =C2=A0 int ma= in() {
=C2=A0 =C2=A0= =C2=A0 =C2=A0 // ...
=C2=A0 =C2=A0 =C2=A0 =C2=A0 for= (int i =3D 0; i < m; i++) {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 int a, b, c;
=C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 std::cin >> a >> b >> c;
<= font face=3D"courier new, monospace">=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 links[i] =3D {c, Coord(), Coord(), a, 0, &comps[b]}; // Non-designa= ted
=C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 links[i] =3D {.src =3D a, .dst =3D &comps[b= ], .bw =3D c}; =C2=A0// Designated
=C2=A0 =C2=A0 =C2=A0 =C2=A0 }
=C2=A0 =C2=A0 =C2=A0 =C2=A0 // ...
=C2=A0 =C2=A0 }
<= div>
Some (likely highly subjective) problems with the non-de= signated syntax:
1. Order dependent (harder to read).
2. Does not scale well, parameter ordering is increasingly difficult to = track when more fields are added.
3. Does not allow explicit initialization of a partial set of fiel= ds. (harder to read, annoying to write)

1, 2: Und= erstanding the designated initializer list assignment requires no declarati= on or parameter order knowledge so the grammar is more context free and the= refore easier to read.

3: You are forced to write an explicit constructor or enum= erate defaults for all fields. An explicit constructor would require extra = boilerplate and introduce another independent order you have to track (more= context). Writing a constructor for a specific way you want to initialize = a class seems like code smell.

So=C2=A0I hope this feature would become standardized.= Thank you for reading my humble opinion.

--

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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/gro= up/std-proposals/.

--

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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-proposa= ls+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-proposals/<= /a>.
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