220 37072 article Path: news.gmane.org!.POSTED!not-for-mail From: olafvdspek@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: const std::map operator [] Date: Mon, 26 Feb 2018 03:04:11 -0800 (PST) Lines: 112 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_2406_2026382015.1519643052056" X-Trace: blaine.gmane.org 1519642933 27982 195.159.176.226 (26 Feb 2018 11:02:13 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 26 Feb 2018 11:02:13 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBC5NB45SSABBBLGTZ7KAKGQEBRRRSLQ@isocpp.org Mon Feb 26 12:02:09 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f71.google.com ([209.85.213.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eqGXn-0006ov-Fa for gclcip-std-proposals@m.gmane.org; Mon, 26 Feb 2018 12:02:07 +0100 Original-Received: by mail-vk0-f71.google.com with SMTP id n23sf4316496vke.14 for ; Mon, 26 Feb 2018 03:04:14 -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: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; bh=RmAfrKlh5+6eJOQXAtk/4nYvD+KP9dgR0up1Jo/lTGE=; b=rxkt7N28mdAHSIPZuc8y5FcoKhYUxDUhdYTw8YTUpLAtOPoE7sz3TRyydMRQ2cjj7r tdasTHzZzrWM8Pj+xL368pRw5oS4ROJRtWxXYAmQZlyp9j8QeK6LKlwpIKVpyjdgIHFD AfM+N3YHgTh/+t7voV/nxiMYVsLiXJdp4HgeT5ksWRENLvsd2Kwgvfu7R2z5z7B6xQlt b2Uyy5BkB7uWdzP2vA+wO7EAN+CRJ5cIKpU3+BF6pVMBwniHYuu0ZgZh0QRSlbzPhsbu pQgBBdMAH4zvNGLUA5Whg9AlyE3DFnyHIVWOp/u8+njGOQ/Vly7CfCeMF9PYvFuvGpm7 Swdw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to: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; bh=RmAfrKlh5+6eJOQXAtk/4nYvD+KP9dgR0up1Jo/lTGE=; b=ayPpRICODwXWIAxsKfcRAdfW0+Kl2us7B82ENTX0K6oIiYHIDs2xqUz1bb+1t42Sq2 if3mYARJBuptRm55G95vzXgW3Vv+B/9d6gfUk7g9JFp6z57qhENd/MUjGSLZhg0THUzY ZrlBUGDHScTRaNjoqBhzjYOwcqhSSB6TPOX/CMeC8WmdCsJoayNLKtwpsHLxpHCBuB4L alEy0+gg9q/YY5g+gqlNecdfk1RGsNTBPi7zFnQUXXCEv1iVbmjPpBjTjwtTkBdfPsPV oezF9EyjnAE3uwJSgVpsbauc1b/4gixny9rVm9o3ninLUzfoaaNoIxIixJBULu7pFvye pJbw== 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:in-reply-to:references :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=RmAfrKlh5+6eJOQXAtk/4nYvD+KP9dgR0up1Jo/lTGE=; b=fnqr/dHktZek+BXHPlr+93i4+qealNcReP6Rz/+/HBK290LdEWZ/hKR4f24rUfTbMl aoHS47YXhmkHtKj3JTpqlf/ExfV+C7fKBMqHxcIM8We+YODoroS54msgg02zx+O9yhXw CNFxeh011XOSvW7WGVdv2AXRCjvIDxLqg1ar1eAgnjnyfI8Ey5MUBPT3O7L/Tc0I8PJM pcn9RaR7YrcelTTxNkOxb1lCSATBIQBHw0dzK4TKtsvJ6E8vWEr3RF3ZSCHn0IzhrVdp 2NOC0IKc/H1IFqw0+J/sTXNmPPOiUSAmND4G7TmbfowgBAv8bWDdP/IBtoyltrTHPYVR ZThw== X-Gm-Message-State: APf1xPD0qMeGvDs6v7ygzhi7FkZuwfvrLE3T96KJVIV+BxIyruDz3xKY VqK8l+kwXHUPBd6KLlnyhBucRA== X-Google-Smtp-Source: AG47ELs+psOT79CnFnl2kUqxQHGm+ehlfD7Ez/v4np6zhcizfIq5cSsTbDArnUWO1sanBPXtYprMHw== X-Received: by 10.31.131.20 with SMTP id f20mr4800255vkd.87.1519643053824; Mon, 26 Feb 2018 03:04:13 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.31.158.3 with SMTP id h3ls4698074vke.11.gmail; Mon, 26 Feb 2018 03:04:12 -0800 (PST) X-Received: by 10.31.67.71 with SMTP id q68mr1075304vka.9.1519643052546; Mon, 26 Feb 2018 03:04:12 -0800 (PST) In-Reply-To: X-Original-Sender: olafvdspek@gmail.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:37072 Archived-At: ------=_Part_2406_2026382015.1519643052056 Content-Type: multipart/alternative; boundary="----=_Part_2407_1973863748.1519643052057" ------=_Part_2407_1973863748.1519643052057 Content-Type: text/plain; charset="UTF-8" Op zondag 5 november 2017 00:18:59 UTC+1 schreef Cleiton Santoia: > > What about include a 'const operator []' in std::map that returns a > std::optional instead a reference to T ? > > std::optional< std::reference_wrapper< T > > operator[] (const Key& key) > const { ... } > > Maybe this is a case for committee consider std::optional for references > > std::optional< T& > operator[] (const Key& key) const { ... } > > A wrapper returning second_type* is so much easier. See my find_ptr and friends. const typename T::value_type::second_type* find_ptr(const T& c, const U& v) https://github.com/OlafvdSpek/xbt/blob/master/misc/xbt/find_ptr.h -- 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/f18af735-cbd2-48ce-b4c4-42a3d320cdeb%40isocpp.org. ------=_Part_2407_1973863748.1519643052057 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Op zondag 5 november 2017 00:18:59 UTC+1 schreef Cleiton S= antoia:
What a= bout include a 'const operator []' in std::map that returns a std::= optional instead a reference to T ?

std::optional< std::reference_wrapper< T >= ; > operator[] (const Key& key) const { ... }

Maybe this is= a case for committee consider std::optional for references
<= br>
std::optional<= ; T& > operator[] (const Key& key) const { ... }=C2=A0


A wrapper retu= rning=C2=A0second_type* is so much easier. See my find_= ptr and friends.

const <= span class=3D"pl-k" style=3D"box-sizing: border-box; color: rgb(215, 58, 73= ); font-family: SFMono-Regular, Consolas, "Liberation Mono", Menl= o, Courier, monospace; font-size: 12px; white-space: pre;">typename<= span style=3D"color: rgb(36, 41, 46); font-family: SFMono-Regular, Consolas= , "Liberation Mono", Menlo, Courier, monospace; font-size: 12px; = white-space: pre;"> T::value_type::second_type* find_ptrconst= T& c, const U& v)

https://github.com/OlafvdSpek/xbt/blob/ma= ster/misc/xbt/find_ptr.h=C2=A0

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