From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on starla X-Spam-Level: X-Spam-Status: No, score=0.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_BL_SPAMCOP_NET,SPF_HELO_PASS, SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6 Received: from nue.mailmanlists.eu (nue.mailmanlists.eu [94.130.110.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id 9A2911F44D for ; Thu, 14 Mar 2024 05:22:41 +0000 (UTC) Authentication-Results: dcvr.yhbt.net; dkim=pass (1024-bit key; secure) header.d=ml.ruby-lang.org header.i=@ml.ruby-lang.org header.a=rsa-sha256 header.s=mail header.b=vEqXkvUL; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=ruby-lang.org header.i=@ruby-lang.org header.a=rsa-sha256 header.s=s1 header.b=XBkxrTCF; dkim-atps=neutral Received: from nue.mailmanlists.eu (localhost [127.0.0.1]) by nue.mailmanlists.eu (Postfix) with ESMTP id A7E1E832BD; Thu, 14 Mar 2024 05:22:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ml.ruby-lang.org; s=mail; t=1710393753; bh=fISs+5keRO7yG5O5CJv+ZUWx0RWNNJuaYgeZpDv2GbU=; h=Date:References:To:Reply-To:Subject:List-Id:List-Archive: List-Help:List-Owner:List-Post:List-Subscribe:List-Unsubscribe: From:Cc:From; b=vEqXkvULcuxlF90HDkZ7eRffzaqww7gVmaO8QG9qcJxGlBxkfcj0GiR9oWdDowG2R CaFxTrWDwjMJMLDYBoJF7dDdBIuG54FltWp8r/nbJvfvF6QjEnwXm7UKzaYIo5ysaZ HiAUXJbd9F394sBvWCjr8u7bziU9TsEvE1Zvc+O4= Received: from s.csnrwnwx.outbound-mail.sendgrid.net (s.csnrwnwx.outbound-mail.sendgrid.net [198.37.146.154]) by nue.mailmanlists.eu (Postfix) with ESMTPS id 814E583180 for ; Thu, 14 Mar 2024 05:22:30 +0000 (UTC) Authentication-Results: nue.mailmanlists.eu; dkim=pass (2048-bit key; unprotected) header.d=ruby-lang.org header.i=@ruby-lang.org header.a=rsa-sha256 header.s=s1 header.b=XBkxrTCF; dkim-atps=neutral DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ruby-lang.org; h=from:references:subject:mime-version:content-type: content-transfer-encoding:list-id:to:cc:content-type:from:subject:to; s=s1; bh=LqpF0aiMSB6JV0YZzZqxyveKVaxfj7pAJuLEMBzBghU=; b=XBkxrTCFzEYVGQHZkPcN2lS1y9FEtEZ83IaEuztqclbnSy5Tc/Xx/qLqR5rPidSBpHfW fALODzxq5OJTyzyGF4zI+m6ekA45b/idlYzhq65gAmHpie5Os6LEKcljDw7jR9jjeMLkTC tPJPPYHBWYrdUHT6OArZJ0RgcKLTFuvyOfqhSmsF2Ts0r6QMD0APZplHImD7btZfMPj9ko kZDnnDZeIZjWBoKKk+4ZsTfH3egIK5ETMMGj5VwqlrA7lDr4GgIX5S4vRyk2v1F937q52G 3qxh0vFVV8LVclgz/FXsgt6EV8ESzDwr5p1TYGko6fknpJM2+fid5kXuW/P04aDw== Received: by recvd-7ffbd89f59-m7f7c with SMTP id recvd-7ffbd89f59-m7f7c-1-65F28994-E 2024-03-14 05:22:28.572440509 +0000 UTC m=+1236799.900415753 Received: from herokuapp.com (unknown) by geopod-ismtpd-11 (SG) with ESMTP id IjeAIvugSU2q_z3j1lkQAA for ; Thu, 14 Mar 2024 05:22:28.485 +0000 (UTC) Date: Thu, 14 Mar 2024 05:22:28 +0000 (UTC) Message-ID: References: Mime-Version: 1.0 X-Redmine-Project: ruby-master X-Redmine-Issue-Tracker: Feature X-Redmine-Issue-Id: 20300 X-Redmine-Issue-Author: AMomchilov X-Redmine-Issue-Priority: Normal X-Redmine-Sender: nobu X-Mailer: Redmine X-Redmine-Host: bugs.ruby-lang.org X-Redmine-Site: Ruby Issue Tracking System X-Auto-Response-Suppress: All Auto-Submitted: auto-generated X-Redmine-MailingListIntegration-Message-Ids: 93702 X-SG-EID: =?us-ascii?Q?u001=2E5PtzXJ23KrYzgM1nrOIr+EQ222PyrDaWSg0Er8CZ8tP86xyXmBM81zBKD?= =?us-ascii?Q?HreavdFYMbHjxXOR6UPMkt=2Fu9CyBIp6y52n8D2y?= =?us-ascii?Q?qA9zqurrgUdYYACtc2xoVblA3rFKQz+y2LiCEL9?= =?us-ascii?Q?s26HR1xRXDi153sVqcXMvfUuxbyzwU38TN6K4fb?= =?us-ascii?Q?=2FQoIbbIfMTE26NdTqXTPCpSyDyNDev81SIFVxK=2F?= =?us-ascii?Q?jyjxYlhCKpmpT354ZaxB5x5JH4cQZ=2F4Pe17ObNo?= =?us-ascii?Q?IQSiDJZnqTS9fdCqHoa5fMVSgQ=3D=3D?= To: ruby-core@ml.ruby-lang.org X-Entity-ID: u001.I8uzylDtAfgbeCOeLBYDww== Message-ID-Hash: CBSBTORIEQGF5AWC2BOJRPMOI3ZBWXJH X-Message-ID-Hash: CBSBTORIEQGF5AWC2BOJRPMOI3ZBWXJH X-MailFrom: bounces+313651-b711-ruby-core=ml.ruby-lang.org@em5188.ruby-lang.org X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.3 Precedence: list Reply-To: Ruby developers Subject: [ruby-core:117136] [Ruby master Feature#20300] Hash: set value and get pre-existing value in one call List-Id: Ruby developers Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: From: "nobu (Nobuyoshi Nakada) via ruby-core" Cc: "nobu (Nobuyoshi Nakada)" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Issue #20300 has been updated by nobu (Nobuyoshi Nakada). I want `ENV.exchange_value` rather than `Hash#exchange_value`. ---------------------------------------- Feature #20300: Hash: set value and get pre-existing value in one call https://bugs.ruby-lang.org/issues/20300#change-107215 * Author: AMomchilov (Alexander Momchilov) * Status: Open ---------------------------------------- When using a Hash, sometimes you want to set a new value, **and** see what was already there. Today, you **have** to do this in two steps: ```ruby h = { k: "old value" } # 1. Do a look-up for `:k`. old_value = h[:k] # 2. Do another look-up for `:k`, even though we just did that! h[:k] = "new value" use(old_value) ``` This requires two separate `Hash` look-ups for `:k`. This is fine for symbols, but is expensive if computing `#hash` or `#eql?` is expensive for the key. It's impossible to work around this today from pure Ruby code. One example use case is `Set#add?`. See https://bugs.ruby-lang.org/issues/20301 for more details. I propose adding `Hash#exchange_value`, which has semantics are similar to this Ruby snippet: ```ruby class Hash # Exact method name TBD. def exchange_value(key, new_value) old_value = self[key] self[key] = new_value old_value end end ``` ... except it'll be implemented in C, with modifications to `tbl_update` that achieves this with a hash-lookup. I'm opening to alternative name suggestions. @nobu came up with `exchange_value`, which I think is great. Here's a PR with a PoC implementation: https://github.com/ruby/ruby/pull/10092 ```ruby h = { k: "old value" } # Does only a single hash look-up old_value = h.exchange_value(:k, "new value") use(old_value) ``` -- https://bugs.ruby-lang.org/ ______________________________________________ ruby-core mailing list -- ruby-core@ml.ruby-lang.org To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org ruby-core info -- https://ml.ruby-lang.org/mailman3/postorius/lists/ruby-core.ml.ruby-lang.org/