220 8681 article Path: news.gmane.org!not-for-mail From: abolz.lists@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: string_view::is_null() Date: Sat, 18 Jan 2014 07:30:17 -0800 (PST) Lines: 80 Approved: news@gmane.org Message-ID: References: <8045a4d2-721d-4725-8bb7-7a91b6f53ec8@isocpp.org> <186E0927-C962-4E34-AED0-E7509DD1F0A0@gmail.com> <7aad44d8-6b4e-438a-b309-bd898b994b34@isocpp.org> <9C2C439F-7983-4224-B272-53CAD0E2E456@gmail.com> <8E74B747-7450-41E0-8D1E-48C2D6F81535@gmail.com> <3a3d55c0-20cb-40ff-ae46-84663d21f44d@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_327_24944384.1390059017415" X-Trace: ger.gmane.org 1390059015 29967 80.91.229.3 (18 Jan 2014 15:30:15 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 18 Jan 2014 15:30:15 +0000 (UTC) Cc: gornishanov@gmail.com To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCAJPLFFWYPBBCN45KLAKGQEYESA3UI@isocpp.org Sat Jan 18 16:30:20 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ob0-f198.google.com ([209.85.214.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1W4Xql-0006Qc-Ms for gclcip-std-proposals@m.gmane.org; Sat, 18 Jan 2014 16:30:20 +0100 Original-Received: by mail-ob0-f198.google.com with SMTP id wp4sf2051006obc.9 for ; Sat, 18 Jan 2014 07:30:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=RTrqbg01nKXAuhteHQZuMeN1Ppu4eFejr+wfMaSj5SY=; b=s/Fx/9JmtKs5iCYMGSnC1f37JAeJCd53OmzfVe2kgLciKrXAwbKFljrEZw1WNWj6b+ Gk7RXOkthxSYNW8QC8R5fHwB9aFpqJu3ph9FTxzEteTdtAHmGK1hKFpdYfJ6m2f+LYLg kMVKFW58v8c1C2WN+WHh1S/Pgi7zvxF8ozu3Vv/pj7dbQHbn36467KzzxJRah6p5yphb hqX/M3s31CBEo/gr3B8MORFT57ZMu3KPEJxkMs00HL1pcr6I1oUopqBYaBOGukJpR8g8 K5DNWiVRxaznIxHo6Ezja4DkCCq2wY98D1Y3Cff7MyYgNqhEFEW6XCMeyQ1XbPqn4ZHi fDDw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:cc:message-id:in-reply-to :references:subject:mime-version:x-original-sender:reply-to :precedence:mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=RTrqbg01nKXAuhteHQZuMeN1Ppu4eFejr+wfMaSj5SY=; b=KhogRflLEgVchIX9NWsuyE+fCsR8TCMXK2pCRXvWREuu+eAjFt7uvT4xfUxcAzOlH9 jNNnuJq0XGkCRB49+EGwET2YCAe3h9Vngjo/4RB7BSvLplF5+eBhDcpYh7OO+UpJoK5K GZ3h+nhdFpMFjg7JU0A4XEZnp/t1tNFw/7K/yYC0s8fYV2EO04gYLDIii6vrPIwmoygO FyhuoVfOp+PQielZAvbBYLM2Oa4esrI+vjtaBNYJy8gbaH1+VD/0pKS+bUsk564i18qf VCac90CGLzX6M3FAwD3LJyAmIdwrs7ozh8wIT6I4GrdIi5LlZqZgVMCBErDdtu8Kx40B HgPw== X-Gm-Message-State: ALoCoQkWNl+J3hARrEpKIOpOoTqNDlrws+AbzrW0st0slXSc7ZGXf92yyXQI5ncBUeWeNNsIr/nK X-Received: by 10.182.126.137 with SMTP id my9mr3099368obb.13.1390059018428; Sat, 18 Jan 2014 07:30:18 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.17.196 with SMTP id q4ls1452245qed.11.gmail; Sat, 18 Jan 2014 07:30:17 -0800 (PST) X-Received: by 10.140.102.35 with SMTP id v32mr11433qge.26.1390059017811; Sat, 18 Jan 2014 07:30:17 -0800 (PST) In-Reply-To: <3a3d55c0-20cb-40ff-ae46-84663d21f44d@isocpp.org> X-Original-Sender: abolzlists@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:8681 Archived-At: ------=_Part_327_24944384.1390059017415 Content-Type: text/plain; charset=UTF-8 Am Samstag, 18. Januar 2014 00:10:41 UTC+1 schrieb gorni...@gmail.com: > > What if string_view provides a specialization for optional>? > > That way optional can be implemented very efficiently by > checking if sv.begin() == nullptr and does not consume any extra storage. > An extra benefit is that we have clear distinction between nullable types > (optional) and regular types, int, vector, string_view, etc. > > Will this solution satisfy the original poster? > An (unspecialized) optional is not always an option. E.g. I can't simply change a function like void f(char const* s) {} to void f(optional s) {} because I can no longer write f("hello"). So the specialization should be implicitly constructible from a char array. And then an optional constructed from a nullptr should be an uninitialized optional since there are no preconditions on f, I should be able to write f(getenv("not-an-env-var")). -- --- 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/. ------=_Part_327_24944384.1390059017415 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Am Samstag, 18. Januar 2014 00:10:41 UTC+1 schrieb gorni..= ..@gmail.com:
What if stri= ng_view provides a specialization for optional<string_view<>>?<= /div>

That way optional<string_view> can be implem= ented very efficiently by checking if sv.begin() =3D=3D nullptr and does no= t consume any extra storage. An extra benefit is that we have clear distinc= tion between nullable types (optional<T>) and regular types, int, vec= tor, string_view, etc.

Will this solution satisfy = the original poster?

An (un= specialized) optional<string_view> is not always an option. E.g. I ca= n't simply change a function like

void f(char= const* s) {}

to

void f(o= ptional<string_view> s) {}

because I can no = longer write f("hello"). So the specialization should be implicitly constru= ctible from a char array.
And then an optional<string_vie= w> constructed from a nullptr should be an uninitialized optional since = there
are no preconditions on f, I should be able to write f(gete= nv("not-an-env-var")).

--
 
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