220 41574 <566197ea-a415-4d2d-9adc-b2a2ff26bdf9@isocpp.org> article Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: =?UTF-8?Q?=27Thomas_K=C3=B6ppe=27_via_ISO_C=2B=2B_Standard_=2D_Future_Proposals?= Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: operator[]= (array subscript assignment operator) Date: Sun, 17 Mar 2019 12:00:14 -0700 (PDT) Approved: news@gmane.org Message-ID: <566197ea-a415-4d2d-9adc-b2a2ff26bdf9@isocpp.org> References: <39460c2e-f24c-4819-8678-267387948e69@isocpp.org> Reply-To: std-proposals@isocpp.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1270_2047099319.1552849214526" Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="59168"; mail-complaints-to="usenet@blaine.gmane.org" Cc: wpmgprostotema@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDH3JAEPRQFBBQFSXLSAKGQEWMIK3VI@isocpp.org Sun Mar 17 20:00:20 2019 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw1-f71.google.com ([209.85.161.71]) by blaine.gmane.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.89) (envelope-from ) id 1h5b19-000FHb-5m for gclcip-std-proposals@m.gmane.org; Sun, 17 Mar 2019 20:00:19 +0100 Original-Received: by mail-yw1-f71.google.com with SMTP id d64sf19515252ywa.17 for ; Sun, 17 Mar 2019 12:00:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; 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; bh=xkMZnZHrGUnpDofPXS5lmsPNzlwg5dbIA1nqdIedAYo=; b=Dtu61h80W1dya90+EvmFy2wy8+XTAKvT+RMMSph23JvnNLQuhv8S8Ma4EyZCbUoIxa lPKSMvQ8Yfvg6DFUI58iDug3/cUUM0joF0kO+OX7hoECVjfN6JfxXWn7oBNydsNdjpjU bvmAZ2fhJuk7k6iJAHkuaUL8PCk0TOxKN8sooM9n8TGjDKl3FdfCt6dtCzmyndxR5nQX 9uKnMMhIGfhgimwx2lRaX5FbBFVlqVOSEQ4/5EqT6EPb3Dp+uBas7CdOL2EUEwcbGotx Wf2xJVp761C8ma3HIbJBM39oAo2TIb2rgXixRqAJAXCgHqiTas2Zx0Zdrft3Khmcwz8J jrrw== 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:cc: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=xkMZnZHrGUnpDofPXS5lmsPNzlwg5dbIA1nqdIedAYo=; b=gL5zK1hxVqO8Vpp8mYHOeDFEsj2SrxMdqHtE/3ead/r860KWl0IFOTNdSm/ayvME5X vsMtrq/Vs4X7VJPZhAab99YpSuE2pK/w/P88dAyAc/3QmsgoIqx7UEwUfxsJOrx11QzD dNylEq2MOcu5ke39Qt3eF041VFK87021+jem1uvJhositnjup+AMZ27ApsJaAL3KNBPC vmFoPTrPPfctEHRsOHD+yyTsmaVPIr7zUJ3/SgDcqbpIUwlKO4xk3wW5VEcMRKstk5el cuzoQafPo3kzmITZs0WMcQwL6JP+mOkJgbX4RRsdnc9TwnC7bNnPLYVhNARJPKzoYsF5 Ao0w== X-Gm-Message-State: APjAAAV8X5kK92XcQ1pnANG0nj+MgIpGOrvFGNq+T6WNijeR3xQwf5cH AcG8OTaYbuaUqOW0U9oVURf9dQ== X-Google-Smtp-Source: APXvYqwPOrwMqROXjsYeLqK7o88mshPmPnKHsT6z6xkIQIDf0Nn6G1MUAdLauNu9gNjzdlAPShuR6w== X-Received: by 2002:a25:1c2:: with SMTP id 185mr8031044ybb.87.1552849217692; Sun, 17 Mar 2019 12:00:17 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a25:1384:: with SMTP id 126ls3152434ybt.1.gmail; Sun, 17 Mar 2019 12:00:15 -0700 (PDT) X-Received: by 2002:a25:6d46:: with SMTP id i67mr11747960ybc.384.1552849215456; Sun, 17 Mar 2019 12:00:15 -0700 (PDT) In-Reply-To: <39460c2e-f24c-4819-8678-267387948e69@isocpp.org> X-Original-Sender: tkoeppe@google.com X-Original-From: =?UTF-8?Q?Thomas_K=C3=B6ppe?= 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:41574 Archived-At: ------=_Part_1270_2047099319.1552849214526 Content-Type: multipart/alternative; boundary="----=_Part_1271_1103837066.1552849214527" ------=_Part_1271_1103837066.1552849214527 Content-Type: text/plain; charset="UTF-8" A few thoughts on proxies, in a modern light: - We should probably have "proxy invalidation" rules. It seems tricky to implement something like looking up an existing value into a proxy, then allowing an interleaving deletion of that element, and then still letting that proxy do something useful. - That said, the proxy could have a two-fold nature: if the key was found, it stores only the relevant iterator. If the key was not found, it stores a special kind of *node-handle* where the mapped-element isn't constructed yet, along with relevant hint information (a lower-bound iterator for ordered maps, and a precomputed hash for unordered maps). Having the *node-handle* solves the problem of retaining the key for later use without making copies or having dangling references. Upon assignment, the mapped-element is constructed in-place and the node handle is inserted. -- 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/566197ea-a415-4d2d-9adc-b2a2ff26bdf9%40isocpp.org. ------=_Part_1271_1103837066.1552849214527 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
A few thoughts on proxies, in a modern light:
  • = We should probably have "proxy invalidation" rules. It seems tric= ky to implement something like looking up an existing value into a proxy, t= hen allowing an interleaving deletion of that element, and then still letti= ng that proxy do something useful.
  • That said, the proxy could have = a two-fold nature: if the key was found, it stores only the relevant iterat= or. If the key was not found, it stores a special kind of=C2=A0node-hand= le where the mapped-element isn't constructed yet, along with relev= ant hint information (a lower-bound iterator for ordered maps, and a precom= puted hash for unordered maps). Having the node-handle solves the pr= oblem of retaining the key for later use without making copies or having da= ngling references. Upon assignment, the mapped-element is constructed in-pl= ace and the node handle is inserted.

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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/566197ea-a415-4d2d-9adc-b2a2ff26bdf9= %40isocpp.org.
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