220 33344 article Path: news.gmane.org!.POSTED!not-for-mail From: Manuel Bergler Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Trait for arithmetic types similar to std::chrono::treat_as_floating_point for the use in other parts of the library Date: Wed, 26 Jul 2017 18:14:20 +0200 Lines: 121 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/alternative; boundary="001a113db9a09a292805553abd07" X-Trace: blaine.gmane.org 1501085664 3558 195.159.176.226 (26 Jul 2017 16:14:24 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 26 Jul 2017 16:14:24 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDOZBAUFX4MRBXX74LFQKGQEGHLJ77A@isocpp.org Wed Jul 26 18:14:19 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qk0-f198.google.com ([209.85.220.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1daOx0-0000YH-7s for gclcip-std-proposals@m.gmane.org; Wed, 26 Jul 2017 18:14:18 +0200 Original-Received: by mail-qk0-f198.google.com with SMTP id s18sf87697490qks.4 for ; Wed, 26 Jul 2017 09:14:24 -0700 (PDT) ARC-Seal: i=2; a=rsa-sha256; t=1501085663; cv=pass; d=google.com; s=arc-20160816; b=a43QhdENgXW6yHPXowI3oGVFy23Ohct4rVd6jZ5HTLbU+YHYLvV4KOUT8TiwKdIXbF 9u893pJcqpFrodyPJEfqUQ9et4NhEQl0Viy398XwDVf+S6znJYcDCgHYZsb3Zlit1KBK cXmNxXAcO/reP/mlomsgmu6alVfge12lDnK4usrPw8mmsaswKbqcrqxPUIoF73vzY+Ca QTk/KKBgUZKT9JavQp6CYnf77SMk5ljTETe6GmxLQhBbXtgka/8jNaFiIlHqeSRIh4Qh +jGQj2naw/MLe3hTCo6zSRM7brz5XLYzakZON2zNipbvvjgpwK4XcWrSUdcTiDd5aKtj B7nQ== ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post :list-id:mailing-list:precedence:reply-to:to:subject:message-id:date :from:mime-version:arc-authentication-results:arc-message-signature :dkim-signature:arc-authentication-results; bh=Ez6aRSCGJSho8NKo0lB//QfFclg0ZABAIkNmYsNpaWA=; b=U6moKLQ/sgEBNjnnnStoF9DRAbGKFbtDdK4W07ofB+u/wI5Z82vun+4FG3rmgWGw9v 9u7J9RVjCQ7EQEzyzJgBfLPXC0B37tWp07iK8E8LwewvxtLLyRhQYxgj8ieBfiALl9SW jgwak5MuJH/9eUoAW2OlgW1ziB1FuSVGj4pQxan1qvbcQm+HPPCkT/DXT9wSn+92umQL RJVXpWXosxjMDpYlqFdv2+B9XrRakB2oDbcVUI56gQw1gqUJAFx1URG9hKibN+w/fw9s wLlEo3/1E45Xpp6PbEa4Y4tMryXQkTB0Pd3sonsvJUCynCrDy3SBfrw2w3lbSGdPTsfG Zp4Q== ARC-Authentication-Results: i=2; mx.google.com; dkim=pass header.i=@gmail.com header.b=LjyyCjh1; spf=pass (google.com: domain of berglerma@gmail.com designates 2607:f8b0:4003:c06::22d as permitted sender) smtp.mailfrom=berglerma@gmail.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=mime-version:from:date:message-id:subject:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=Ez6aRSCGJSho8NKo0lB//QfFclg0ZABAIkNmYsNpaWA=; b=TMqESE/gxklqdL3bBYrvzYbvj1jN2CNIm33oC1NxbdxgqdBoOMtpLJVejM/ohSad5J mZr7HmXkVDDsO5eiHdF+mvwat4kjMDzOy0cFIPn/Eec7u6alRo+twsnaEw0BpbkOqaHU OR2qvngLdhi7jMgDcA7/atT7UqLHBJjWXqXYtXBz+PVaupCy5RKnOVTYkFWKbKV9XBw3 L8t6WyUyiD+XUkwaDAdoIPUtQfKV1JCfWq2zJzWjh/ybE6dO2dy51HNQMHblB3L0ka/c D8d/x7Q4JrMbFBBwuoC3dla79IPQIwqymrO3G1sSjY2I88WazADKfe3hj7nHvH3y19pE a0KA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:from:date:message-id:subject:to :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=Ez6aRSCGJSho8NKo0lB//QfFclg0ZABAIkNmYsNpaWA=; b=tU5fvQADj4mORskdcQ7orYOGa5tlJpIu0Tkgdcq6Y8uNmg3dfRyob4TrQnqjuwUkFA H7a1p6sz+LbCpMEPzQO88UYACkhaSFZzZCC9cb8NS727QukcMxha0+8yj/Sq/GAeLlyM P/MTYpyQB2EKTlLqriOvZbCRtM8ZaKbCpAUeWIk1d5XxzXPa+tQh/Xe0m8xHzOaMssZJ JmSvl6zET0841MFYEv8yruFDxs0vRfiIWmzsVRiMUC1DEudVu55TQFUky5WqjNhkKWHZ cV8qdopUxTUf0AU2zz/tmUJTqHb5rnABwa3Al3raqzk6P84tKiJiTxBsYDSUDAI+qL7u qP9g== X-Gm-Message-State: AIVw110XVka3VPhMLkTVPEkXV6tOAigz2rQpGIeJPO+SuHWTMyY9qcep +/8/7BEtckg4m3i2 X-Received: by 10.200.32.129 with SMTP id 1mr947864qtd.105.1501085663800; Wed, 26 Jul 2017 09:14:23 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.12.201 with SMTP id 70ls758484iom.22.gmail; Wed, 26 Jul 2017 09:14:21 -0700 (PDT) X-Received: by 10.202.76.214 with SMTP id z205mr1389498oia.215.1501085661647; Wed, 26 Jul 2017 09:14:21 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1501085661; cv=none; d=google.com; s=arc-20160816; b=E/A/TXgi0q6AECOR5uHp78p8Hi4w6Y0bVkskHiVVMEhRfQVmOJkfhbutHeRnhSLlKd ACwi9bm5bAHmJSfZcg2b4RPo646zAWwNvjFBuy/j8XkR62NkmR9z9HqB3VwHKrhn6moA 8tZvzxPomjRStxmW/Y0xSA1EePSbCVkr2mXZh1QsIcKWTV9PiytI283SXK9J38pl0wM9 7njYdLMbi8lBKzB4UpfO/i/GR7NXm9T6kRMiztcfrTGEPd2iIvebWJYnF4r1txGtnPiD VP+rz85ws2c9QiqjEht6luYTneN5YFoLDFeviHbxR2yVCUb7VFJ8b7GJivkcj0ASYQmf scxg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=to:subject:message-id:date:from:mime-version:dkim-signature :arc-authentication-results; bh=qFJOa1vgX4nLGcWFfVXdQ8Em+erUU2IMuEO5SQnGy3w=; b=pTMPsAhyjoSkNHM8cKzLCNHdNjsEm7jZJ3fUZis3Cx6tZ8Oq0xjx+7W4E7JmIJBz/i hIK01Dll+LYT0QTJPVXixLu/a0qAdy97zPDfJai0MCkUr4MgHey5ojNyTfH8YRPv1/8U utOfsH63xEAb8nJGPYLX2hgYyic7ytNvFqtoTmLi72IP7c41SG7GYHFDkrymr45cWx0F 9us3fRVng9DJivKO2cx/gRTFqo6izB7iLooB+xmTTamcQkmjroYBdwr5SMxNKzbFr5q7 qJfeZulwvAq8/KR2JFUWHvi39Z4okHOjuuRid7XHycO+BQFEMd9MvLC8J7bpePr9YKig /PdQ== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.b=LjyyCjh1; spf=pass (google.com: domain of berglerma@gmail.com designates 2607:f8b0:4003:c06::22d as permitted sender) smtp.mailfrom=berglerma@gmail.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=gmail.com Original-Received: from mail-oi0-x22d.google.com (mail-oi0-x22d.google.com. [2607:f8b0:4003:c06::22d]) by mx.google.com with ESMTPS id t191si9287685oit.12.2017.07.26.09.14.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 26 Jul 2017 09:14:21 -0700 (PDT) Received-SPF: pass (google.com: domain of berglerma@gmail.com designates 2607:f8b0:4003:c06::22d as permitted sender) client-ip=2607:f8b0:4003:c06::22d; Original-Received: by mail-oi0-x22d.google.com with SMTP id g131so84521329oic.3 for ; Wed, 26 Jul 2017 09:14:21 -0700 (PDT) X-Received: by 10.202.10.221 with SMTP id k90mr1196963oiy.245.1501085661011; Wed, 26 Jul 2017 09:14:21 -0700 (PDT) Original-Received: by 10.74.100.85 with HTTP; Wed, 26 Jul 2017 09:14:20 -0700 (PDT) X-Original-Sender: berglerma@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.b=LjyyCjh1; spf=pass (google.com: domain of berglerma@gmail.com designates 2607:f8b0:4003:c06::22d as permitted sender) smtp.mailfrom=berglerma@gmail.com; dmarc=pass (p=NONE sp=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-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:33344 Archived-At: --001a113db9a09a292805553abd07 Content-Type: text/plain; charset="UTF-8" Hi everyone, I recently came across an easily fixed issue with the distributions producing real values (in my particular case std::normal_distribution): While all of these have a template parameter to allow for different floating point types, they are specified in terms of std::is_floating_point - which users are not allowed to specialize. This makes it cumbersome to use it with custom arithmetic types. In my case I needed a random std::chrono::duration. Due to the limitation on types satisfying std::is_floating_point you can't just create a std::normal_distribution>, but instead first have to get the counts for the mean and the standard deviation out of existing std::chrono::duration objects out, create a distribution using these values, and finally pack the value obtained by using its operator() back into a std::chrono::duration object at every site that uses the distribution. However, allowing only float, double or long double is not a restriction of the implementation (at least in the libstdc++ one I tested). As a matter of fact, just specializing std::is_floating_point for std::chrono::duration - even though it is not allowed and thus undefined behaviour - makes ```` using milliseconds_d = std::chrono::duration; std::normal_distribution distribution{milliseconds_d{0}, milliseconds_d{1}}; ```` compile and the distribution yields the exact same values as it does for pure doubles. So I was wondering where else in the library these restrictions are kind of arbitrary and if it does make sense to use something like std::chrono::treat_as_floating point in other places of the library. But before searching in all of the STL for components that are unnecessarily restrictive I first wanted to ask for feedback. In light of the work on the Numerics TS as outlined in [P0101r0], which will introduce more arithmetic types to the standard library I think it definitely makes sense to make all kinds of STL components aware of user-defined arithmetic types, but what is your opinion? Best regards Manuel [P0101r0] http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0101r0.html -- 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/CAM76qmvf09dHUx6-9sui_XAA6amObKUjcp_DrEsHXRAJ1qu5pA%40mail.gmail.com. --001a113db9a09a292805553abd07 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Hi everyone,

I recently came across an = easily fixed issue with the <random> distributions producing real val= ues (in my particular case std::normal_distribution): While all of these ha= ve a template parameter to allow for different floating point types, they a= re specified in terms of std::is_floating_point - which users are not allow= ed to specialize.

This makes it cumbersome to use = it with custom arithmetic types. In my case I needed a random std::chrono::= duration<double, std::milli>.=C2=A0

Due to t= he limitation on types satisfying std::is_floating_point you can't just= create a std::normal_distribution<std::chrono::duration<double,= std::milli>>, but instead first have to get the counts for the mean = and the standard deviation out of existing std::chrono::duration<double,= std::milli> objects out, create a distribution using these values, and = finally pack the value obtained by using its operator() back into a std::ch= rono::duration object at every site that uses the distribution.
<= br>
However, allowing only float, double or long double is not a = restriction of the implementation (at least in the libstdc++ one I tested).= As a matter of fact, just specializing std::is_floating_point for std::chr= ono::duration - even though it is not allowed and thus undefined behaviour = - makes=C2=A0
=C2=A0 =C2=A0
=C2=A0 =C2=A0 ````
=C2= =A0 =C2=A0 using milliseconds_d =3D std::chrono::duration<double, std::m= illi>;
=C2=A0 =C2=A0 std::normal_distribution<millisec= onds_d> distribution{milliseconds_d{0}, milliseconds_d{1}};
=C2=A0 =C2=A0 ````

compile and the distribution= yields the exact same values as it does for pure doubles.

So I was wondering where else in the library these restrictions ar= e kind of arbitrary and if it does make sense to use something like std::ch= rono::treat_as_floating point in other places of the library.
But= before searching in all of the STL for components that are unnecessarily r= estrictive I first wanted to ask for feedback.

In = light of the work on the Numerics TS as outlined in [P0101r0], which will i= ntroduce more arithmetic types to the standard library I think it definitel= y makes sense to make all kinds of STL components aware of user-defined ari= thmetic types, but what is your opinion?

Best rega= rds
Manuel =C2=A0


--
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 htt= ps://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAM76qmvf09dHUx6-= 9sui_XAA6amObKUjcp_DrEsHXRAJ1qu5pA%40mail.gmail.com.
--001a113db9a09a292805553abd07-- .