220 31130 article Path: news.gmane.org!.POSTED!not-for-mail From: =?UTF-8?Q?Jens_=C3=85kerblom?= Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Stronger Version of typedef Date: Sat, 25 Feb 2017 03:14:21 -0800 (PST) Lines: 221 Approved: news@gmane.org Message-ID: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_468_818244683.1488021261577" X-Trace: blaine.gmane.org 1488021261 21849 195.159.176.226 (25 Feb 2017 11:14:21 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 25 Feb 2017 11:14:21 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBC2YT3FOXEIBBDWOYXCQKGQENPEBEDA@isocpp.org Sat Feb 25 12:14:17 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ot0-f198.google.com ([74.125.82.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1chaIr-00056n-8r for gclcip-std-proposals@m.gmane.org; Sat, 25 Feb 2017 12:14:17 +0100 Original-Received: by mail-ot0-f198.google.com with SMTP id y13sf68761714oty.2 for ; Sat, 25 Feb 2017 03:14:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:x-spam-checked-in-group :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=/X1KnEH38ORy/Ymrjw8fCFbAy0Bc9tk0uoVMiOfwsDw=; b=W9vvtyqxny+xhJqPH/V76xJl+4uEfmDe8fUtMe244stq9mmoW0FyoljzMG9HyKKL3I bE+lVQDMwxP6fUdipvORn9aVBzW/hO04ZXzsCnsf4TO6ZQVmVbpm9SgBttB8gMS0FPoK W/xUn2ziXQuoGX5HvvMhHYgLXRuSp/ObZNMRc7KnI116mmMPwAJw2RNUpuYRsqevvi35 u8xfJHggmQbPElPHOSfR1z3ycTh+j4Fyhadrbo9d0R5ctAVGHHS+lIqtpjx6ojBElaLU oxwaLVYwJ6BAqSw0HErgoA2GIfWmAkBnQzKVJ9H8z4T3/c+KhtUfKGZoUFQGHQgFgdU3 bgqw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:x-spam-checked-in-group :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=/X1KnEH38ORy/Ymrjw8fCFbAy0Bc9tk0uoVMiOfwsDw=; b=jm6F4s5yaQ0MxTBd/7FW1g9REsYIoQwxxPgK0W4wLJal0v6iZOlZpP0AJVL0TybNF1 IP9CDJOaDQGNanXP0NB55eGFnpSrHFRRYSFlbfFybMtTgX8lfXW9senCbFmNKjATMuLk rqnRFh9tOMd4cvIOpWManGJyptZQaFjlBrlaJkj1VS3QlKPRqZKkD1sXZjKlc/HkTsc8 tvzXjGNvKJ6eobDrBXptADhFtLb4Cmnvfe96IgXVe2HKAUlbiQa9R1Qz4qdSfTmYN6LI lu9CZg0vnUhceI9IxeXtKMHzCZDZCQELXf1yftcaevM92CJa59QM5ourvIZTmEBYIc58 cCIA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=/X1KnEH38ORy/Ymrjw8fCFbAy0Bc9tk0uoVMiOfwsDw=; b=R8c0n5rystU6Ikm8qqEYP3Pll4gjp0R5Y8Q5PKPl8YiRxdY/hu4d9tfSa6ZCZZ4PLz EuEGjfuVWkQeVZihVA4U/DurL6j6tHx1XxY9Oo+bp7movN9CIjjGlw2SAmuCQHShFLWH AMfQI6ldIysu30IwHUJAbEaBXHJIuteHF5b2zzUabPbaGFb77qyGiNhOHkH9OmvZQMty ayC1WO41J1Q/JgXt0IY0nanG6o0AhRtn6XRa4ktVzkmzSWaci1tgL04tin4K4C7tq9Gf Kox05ttxJQaR2xM3vhBpDT2WUhhXqw/wiBlSl9Pa8hmZ+b1D4G9sI1bXK7BDSlb/ZsYG uKtw== X-Gm-Message-State: AMke39kU9ANabQLVSKzCZkAR4kbJakWh0rwEKW7NPt99GTM8VsNxWk53zbFSCq11o3Hw6w== X-Received: by 10.157.50.45 with SMTP id t45mr2557602otc.43.1488021262725; Sat, 25 Feb 2017 03:14:22 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.42.168 with SMTP id e37ls9234646otb.13.gmail; Sat, 25 Feb 2017 03:14:22 -0800 (PST) X-Received: by 10.157.82.86 with SMTP id q22mr516322otg.3.1488021262096; Sat, 25 Feb 2017 03:14:22 -0800 (PST) X-Original-Sender: akerblom.jens@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:31130 Archived-At: ------=_Part_468_818244683.1488021261577 Content-Type: multipart/alternative; boundary="----=_Part_469_593012567.1488021261578" ------=_Part_469_593012567.1488021261578 Content-Type: text/plain; charset=UTF-8 Using typedef can be a very good way of simplifying the code by having the new type name indicate the usage, for example: typedef float radians_t; typedef float degrees_t; typedef int foo_id_t; typedef int bar_id_t; void setAngle(radians_t angle); Foo& getFoo(foo_id_t id); Bar& getBar(bar_id_t bar); However, this is a very weak typing. Consider degrees_t angle = 45.0f; foo_id_t fooId = 5; bar_id_t barId = 8; // These "should" probably all be errors: setAngle(angle); Foo& foo = getFoo(barId); Bar& bar = getBar(fooId); One way to work around this is to create a new type (using struct or class) and implement all functionality of the type you'd like to typedef. This does however force the programmer to create a lot of code and since it's only for catching error cases it doesn't happen that often. Such as: struct radians_t { float v; }; bool operator<(radians_t, radians_t); radians_t operator+(radians_t, radians_t); // etc... struct degrees_t { float v; }; bool operator<(degrees_t, degrees_t); degrees_t operator+(degrees_t, degrees_t); // etc... radians_t angle1; degrees_t angle2; angle1 = angle2; // Error (unless user-defined cast operator exists). Ada has the feature that you can subtype as: type INT is new Integer; a : INT; b : Integer; a := b; <- ERROR Is there any proposal to have a more "strongly typed" version of typedef? Something like the Ada functionality above. -- 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/cb540c63-e37e-4c86-ab7f-6d5791aa70fc%40isocpp.org. ------=_Part_469_593012567.1488021261578 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Using typedef can be a very good way of simplifying the co= de by having the new type name indicate the usage, for example:

typedef float radians_t;
typedef float degrees_t;
= typedef int foo_id_t;
typedef int bar_id_t;

void setAngle(rad= ians_t angle);
Foo& getFoo(foo_id_t id);
Bar& getBar(bar_id_t bar);
=

However, this is a very weak typing. Consider=

degrees_t angle =3D 45.0f= ;
foo_i= d_t fooId = =3D 5;
bar_id_t barId =3D 8;

// These "should" probably all be errors:=
setAngle(angle);
Foo& foo =3D= getFoo(barId);
Bar& bar =3D getBar(fooId);

One way to work around this is to create a new type (using struct or class) and implement all functionality of the type you'd like to typedef. Thi= s does however force the programmer to create a lot of code and since=20 it's only for catching error cases it doesn't happen that often. Su= ch=20 as:

struct radians_t
{
=C2=A0=C2=A0=C2=A0 float v;
};

bool o= perator<(radians_t, radians_t);
radians_t operator+(radians_t,= radians_t);
// etc...

struct degrees_t
{
=C2=A0= =C2=A0=C2=A0 float v;
};

bool operator<(degrees_t, degrees_t);
<= span style=3D"color: #606;" class=3D"styled-by-prettify">degrees_t oper= ator+(degrees_t, degrees_t);
// etc...

radians_t angle1;
degrees_t angle= 2;

angle1 =3D angle2; // Error (unless user-defined cast operator ex= ists).
=

Ada has the feature that you can subtype as:<= br>
t= ype INT is new Integer;
a : INT;
b : Integer;

a :=3D b; <- = ERROR

Is there any proposal to have a more "strongl= y typed" version of typedef? Something like the Ada functionality abov= e.

--
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.
To view this discussion on the web visit https://groups.google.= com/a/isocpp.org/d/msgid/std-proposals/cb540c63-e37e-4c86-ab7f-6d5791aa70fc= %40isocpp.org.
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