220 36865 article Path: news.gmane.org!.POSTED!not-for-mail From: Avi Kivity Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: String interpolation Date: Sun, 11 Feb 2018 15:06:42 +0200 Lines: 464 Approved: news@gmane.org Message-ID: References: <356d5835-f1bf-4699-94f5-0b2d3d0b9c0e@isocpp.org> <25CCF885-86AD-4D51-8F5C-C46376D34DE0@gmail.com> <4890431.TR9UepuQra@tjmaciei-mobl1> <1cdb6300-7397-46d7-bce9-62e6e8dac40b@isocpp.org> <4bce681e-e729-4124-9322-69291fdb6678@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="------------D4C9F3A332FB9B8A35F1ACB7" X-Trace: blaine.gmane.org 1518354298 3513 195.159.176.226 (11 Feb 2018 13:04:58 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 11 Feb 2018 13:04:58 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 To: std-proposals@isocpp.org, Nicol Bolas Original-X-From: std-proposals+bncBDHJFOWD7YCRBZP7QDKAKGQEPNR6HTQ@isocpp.org Sun Feb 11 14:04:53 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f71.google.com ([74.125.82.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ekrJB-0008Gl-Hy for gclcip-std-proposals@m.gmane.org; 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[79.178.1.170]) by smtp.googlemail.com with ESMTPSA id 11sm3517322wmp.36.2018.02.11.05.06.43 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 11 Feb 2018 05:06:43 -0800 (PST) In-Reply-To: Content-Language: en-US X-Original-Sender: avi@scylladb.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@scylladb-com.20150623.gappssmtp.com header.s=20150623 header.b=epRjV7oD; spf=pass (google.com: domain of avi@scylladb.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=avi@scylladb.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:36865 Archived-At: This is a multi-part message in MIME format. --------------D4C9F3A332FB9B8A35F1ACB7 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: quoted-printable On 02/10/2018 07:30 AM, Nicol Bolas wrote: > > > On Friday, February 9, 2018 at 5:12:26 PM UTC-5, Marcin Jaczewski wrote: > > > > On Friday, February 9, 2018 at 10:13:10 PM UTC+1, Jake Arkinstall > wrote: > > > > On 9 Feb 2018 20:51, wrote: > > > Minimal version than could be added to C++ is new string > prefix `F` (because we have `R`, `u`, `u8` and `U` > already, and `$` is outside of source characters) that > enable mixing code with string literals. > As Marcel Kr=C3=BCger wrote, language could transform this > string literal to: > | > F"testA{a}test{{B}}"_x;=3D>operator""_x("testA"_x,a,"test{B}"= _x);//using > same postfix to parse sub-literals > FR"aa(x{b}y)aa"_x;=3D>operator""_x(R"aa(x)aa"_x,b,R"aa(y)aa"_= x);//it > have precedence over `R` prefix > | > > > > Rest will be implemented by library, this mean `F"a {5} > b"` will not compile because there is no matching > operator. stl could add this operator for `s` postfix, > that will use `std::to_string` for conversing all arguments: > | > template > std::stringoperator""s(Parts&&...p){returnstd::to_string(std:= :forward(p))+...;} > > intmain() > { > autox =3DF"Test {{a}} =3D {10+5}"s;//x =3D=3D "Test {a} =3D 1= 5"s > } > | > |No iosteam, and even more it could if someone relay > desire to have localizations: > > | > F"Test {356*10}"_loc("Prod {0} OK!","fr")=3D=3D"Prod 3.560,00 > OK!"; > | > > Only drawback is some template bloat but this is probably > acceptable cost.| > > > This is exactly the kind of thing I'm aiming for, although I > dont believe string conversion and concatenation to be the > final solution - unless my recall of benchmarks is out of > date, streams are faster than string concatenation. > > This being said, similar ideas can be applied to utilise the > fmt library, for example. > > > This is irrelevant, how it will be implemented is QoI, It could be > done using `snprintf`, or even not implemented at all, only prefix > `F`and its transformation is important. > > More I think about this more it look as great addition to language: > | > std::stringa; > intb =3D0; > intc =3D42; > db.run(F"select name as {a}, age as {b} from table where id =3D > {c}"_sql); > > | > > > If how this is implemented is a mere implementation detail, how would=20 > you make it use bound parameters or otherwise sanitize string inputs?=20 > Have we learned nothing from Little Bobby Tables ? > My horrible code injection proposal would make it work. It would=20 transform the thingie above into "prepare_and_execute("select name as ?,=20 age as ? from table where id =3D ?", a, b, c)" (ignoring the bad SQL for a= =20 minute). > Indeed, this seems like a justification to /not/ provide this feature. --=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/ff46a2e5-cf65-7612-a284-6163e53b9bc3%40scylladb.= com. --------------D4C9F3A332FB9B8A35F1ACB7 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On 02/10/2018 07:30 AM, Nicol Bolas wrote:


On Friday, February 9, 2018 at 5:12:26 PM UTC-5, Marcin Jaczewski wrote:


On Friday, February 9, 2018 at 10:13:10 PM UTC+1, Jake Arkinstall wrote:


On 9 Feb 2018 20:51, <inkwizyt.= ...@gmail.com> wrote:

Minimal version than could be added to C++ is new string prefix `F` (because we have `R`, `u`, `u8` and `U` already, and `$` is outside of source characters) that enable mixing code with string literals.
As Marcel Kr=C3=BCger wrote, language could transform this string literal to:
F"testA{a}test{{B}}= "_x; =3D> operator""_x("testA"_x, a, "test{B}"_x); //using same postfix to parse sub-literals
FR"aa= (x{b}y)aa"_x; =3D> operator""_x(R"aa(x)aa"_x, b, R"aa(y)aa"_x); //it have precedence over `R` prefix



Rest will be implemented by library, this mean `F"a {5} b"` will not compile because there is no matching operator. stl could add this operator for `s` postfix, that will use `std::to_string` for conversing all arguments:
template<typename... Parts>
std::= string operator""s(Parts&&... p) { return std::to_string(std::forward<Parts<= span style=3D"color:#660">>(p)) + ...; }

int main()
{
=C2=A0 =C2=A0 auto x =3D F"Test {{a}} =3D {10+5}"s; //x =3D=3D "Test {= a} =3D 15"s
}
No iosteam, and even more it could if someone relay desire to have localizations:

F<= span style=3D"color:#080">"Test {356*10}"<= /span>_loc("Prod {0} OK!", "fr") =3D=3D "Prod 3.560,00 OK!";

Only drawback is some template bloat but this is probably acceptable cost.

This is exactly the kind of thing I'm aiming for, although I dont believe string conversion and concatenation to be the final solution - unless my recall of benchmarks is out of date, streams are faster than string concatenation.

This being said, similar ideas can be applied to utilise the fmt library, for example.
=C2=A0
This is irrelevant, how it will be implemented is QoI, It could be done using `snprintf`, or even not implemented at all, only prefix `F`and its transformation is important.

More I think about this more it look as great addition to language:
std::string a;
int b =3D 0;
int c =3D 42;
db.run(F"select name as {a}, age as {b} from table where id =3D {c}"_sql);


If how this is implemented is a mere implementation detail, how would you make it use bound parameters or otherwise sanitize string inputs? Have we learned nothing from Little Bobby Tables?



My horrible code injection proposal would make it work. It would transform the thingie above into "prepare_and_execute("select name as ?, age as ? from table where id =3D ?", a, b, c)" (ignoring the bad SQL for a minute).





Indeed, this seems like a justification to not provide this feature.

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