220 39855 <698e2fea-a733-33b5-282b-b033fe8b9167@wanadoo.fr> article Path: news.gmane.org!.POSTED!not-for-mail From: "Vicente J. Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: What do we want from named paramaters Date: Fri, 17 Aug 2018 11:33:43 +0200 Lines: 212 Approved: news@gmane.org Message-ID: <698e2fea-a733-33b5-282b-b033fe8b9167@wanadoo.fr> References: <1534441498.3721109.1476442920.71D445BF@webmail.messagingengine.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="------------48E4F9F6805358635CA35F0A" X-Trace: blaine.gmane.org 1534498303 30792 195.159.176.226 (17 Aug 2018 09:31:43 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 17 Aug 2018 09:31:43 +0000 (UTC) User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 To: std-proposals@isocpp.org, Justin Bassett Original-X-From: std-proposals+bncBDH67CONY4PBB6NM3LNQKGQEEF5RIMY@isocpp.org Fri Aug 17 11:31:39 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f72.google.com ([74.125.82.72]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fqb6V-0007q1-A9 for gclcip-std-proposals@m.gmane.org; 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[80.12.242.133]) by mx.google.com with ESMTPS id 197-v6si2646580wmi.183.2018.08.17.02.33.44 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 17 Aug 2018 02:33:44 -0700 (PDT) Received-SPF: neutral (google.com: 80.12.242.133 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.133; Original-Received: from imac-de-vicente-botet-escriba.home ([86.253.39.2]) by mwinf5d46 with ME id Q9Zj1y00802nUfq039ZkxF; Fri, 17 Aug 2018 11:33:44 +0200 X-ME-Helo: imac-de-vicente-botet-escriba.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Fri, 17 Aug 2018 11:33:44 +0200 X-ME-IP: 86.253.39.2 In-Reply-To: Content-Language: en-US X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.133 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) smtp.mailfrom=vicente.botet@wanadoo.fr 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:39855 Archived-At: This is a multi-part message in MIME format. --------------48E4F9F6805358635CA35F0A Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: quoted-printable Le 17/08/2018 =C3=A0 06:39, Justin Bassett a =C3=A9crit=C2=A0: > On Thu, Aug 16, 2018 at 10:45 AM Henry Miller > wrote: > > > In the past couple months I've seen several proposals for names > parameters.=C2=A0 Each with a list of pros and cons, and because ther= e > are cons arguments against them.=C2=A0 I think we need a discussion o= n > what we want assuming some strawman acceptable syntax, and some > thought of how many limitations in corner cases we are willing to > accept. > > I can think of 4 uses for names parameters. (If you don't > understand these I have simple code examples) > 1 . a function with more than one parameter of the same type is > called with the parameters in the wrong order > =C2=A0 =C2=A0 =C2=A0 *=C2=A0 Some people want this to be a compilatio= n error, some > want the compiler to correct the problem and continue > 2. a function wants to take the same type to mean different things > in different contexts > 3. it isn't obvious from the type alone what a parameter means > 4. A function has a bunch of defaulted arguments and you want to > change one of the latter ones without specifying all the others > > First question: is this complete? > Second, which problems are worth solving? > Third, for problems worth solving, which is the better solution, > and how strongly attached to it are you? > > > Some other use cases: > > 5. In tandem with reflection, names could be used for their names. A=20 > formatting library could use this in tandem with reflection:=20 > fmt::format("{sign} {value}", .sign =3D "$", .value =3D 1.34_usd);=20 > Language bindings to e.g. Python could use it to specify names for=20 > parameters=C2=A0=C2=A0(e.g. this could expose the parameter names to the= =20 > language bindings: m.def([](int .a, int .b) { return a + b; }) ) I don't think this is a named parameter use case, even if it look like.=20 Note that the name of the arguments is not given by the parameter name=20 of the function, as it -is a variadic function, but for the name inside=20 the formatting string. So even if I want this to be solved, I don't=20 think it belongs to this feature. > 6. This is a variation on 4. There may not be a bunch of defaulted=20 > arguments, but rather a few expert settings which you want the users=20 > to be able to tweak on rare occasions. Could you elaborate? > 7. bool arguments have meaning. It's pretty well known that something=20 > like file.open("path/to/file.txt", true) is bad, because the bool has=20 > no meaning. But file.open("path/to/file.txt", .append =3D true) isn't so= =20 > bad because the meaning is apparent. Enums currently fill this role. Well, not only bool arguments. int arguments have also meaning. I=20 believe this fall under case 3. Vicente --=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. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/698e2fea-a733-33b5-282b-b033fe8b9167%40wanadoo.f= r. --------------48E4F9F6805358635CA35F0A Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Le 17/08/2018 =C3=A0 06:39, Justin Basse= tt a =C3=A9crit=C2=A0:
On Thu, Aug 16, 2018 at 10:45 AM Henry Miller <hank@millerfarm.com> wrote:

In the past couple months I've seen several proposals for names parameters.=C2=A0 Each with a list of pros and cons, and because there are cons arguments against them.=C2=A0 I think we need a discussion on what we want assuming some strawman acceptable syntax, and some thought of how many limitations in corner cases we are willing to accept.

I can think of 4 uses for names parameters. (If you don't understand these I have simple code examples)
1 . a function with more than one parameter of the same type is called with the parameters in the wrong order
=C2=A0 =C2=A0 =C2=A0 *=C2=A0 Some people want this to be a comp= ilation error, some want the compiler to correct the problem and continue
2. a function wants to take the same type to mean different things in different contexts
3. it isn't obvious from the type alone what a parameter means
4. A function has a bunch of defaulted arguments and you want to change one of the latter ones without specifying all the others

First question: is this complete?
Second, which problems are worth solving?
Third, for problems worth solving, which is the better solution, and how strongly attached to it are you?

Some other use cases:

5. In tandem with reflection, names could be used for their names. A formatting library could use this in tandem with reflection: fmt::forma= t("{sign} {value}", .sign =3D "$", .value =3D 1.34_usd); Languag= e bindings to e.g. Python could use it to specify names for parameters=C2=A0=C2=A0(e.g. this could expose the parameter nam= es to the language bindings: m.de= f([](int .a, int .b) { return a + b; }) )

I don't think this is a named parameter use case, even if it look like. Note that the name of the arguments is not given by the parameter name of the function, as it -is a variadic function, but for the name inside the formatting string. So even if I want this to be solved, I don't think it belongs to this feature.
6. This is a variation on 4. There may not be a bunch of defaulted arguments, but rather a few expert settings which you want the users to be able to tweak on rare occasions.
Could you elaborate?
7. bool arguments have meaning. It's pretty well known that something like file.op= en("path/to/file.txt", true) is bad, because the bool has no meaning. But file.open("path/to/file.txt= ", .append =3D true) isn't so bad because the meaning is apparent. Enums currently fill this role.
Well, not only bool arguments. int arguments have also meaning. I believe this fall under case 3.

Vicente

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