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 autolearn=no autolearn_force=no version=3.4.6 Received: from nue.mailmanlists.eu (nue.mailmanlists.eu [IPv6:2a01:4f8:1c0c:6b10::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id F01C81F44D for ; Wed, 17 Apr 2024 04:30:20 +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=ljUDPMbw; 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=qSeyQ9U0; dkim-atps=neutral Received: from nue.mailmanlists.eu (localhost [127.0.0.1]) by nue.mailmanlists.eu (Postfix) with ESMTP id 5C4408434E; Wed, 17 Apr 2024 04:30:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ml.ruby-lang.org; s=mail; t=1713328213; bh=Eaap1emhIQ17/KqIlbFWM2vjFZiFVbddaxNKzryDABk=; 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=ljUDPMbwTNPzgz0nlY7H52ZA4UKeoYgtmoXTxMhcXPXRs7HxNC630a506G6qfOt4I 2xytlBDfyLewN9W+aqPGUcYuwu2nKkyh1mKR6lDh/gOcaXPBrfhoHWPs07WSAd35Gt VB0COsig7UVmlDn9GXk3uRWfBb1toeEMXVD8qgtw= Received: from s.wrqvtvvn.outbound-mail.sendgrid.net (s.wrqvtvvn.outbound-mail.sendgrid.net [149.72.120.130]) by nue.mailmanlists.eu (Postfix) with ESMTPS id E992D7EE04 for ; Wed, 17 Apr 2024 04:30:10 +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=qSeyQ9U0; 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=+f+ABHBpxTrseLO7gqKFwPLXB1JtczdFwa0qbM9IsIg=; b=qSeyQ9U0FJD5fHCDo0chSfpB/jWww1Yrg/0ssEeiSgai0t2BoOdrnIJDVrMPCqvAmkxr n9ZgrU35IyezKQaB9WEhcYheM1Qan+sFrBFF7BPdF5BiIONbGVN7KQG4gAAH4BPfrfO0eh njc7Afsq9F/ulocBmjvz8qdVswAygqdlmRFDIfY4xfaoJRzJynmGmIdF83nZ1r5TTGkJQj G3EQG6Nl6pmYzvV3Q9h6pqPLRMO2o/+irI58oddkwPKmQqlWyRxFc5Zcl7kqwpCMRHfBZm QZcktkL32KxBjmyUA0avBGyDdynV5IWsbaBHGVlyJ/IkW5Ad3pGRmmmZpXgEYKmw== Received: by recvd-8c7b9fb4f-z2kmm with SMTP id recvd-8c7b9fb4f-z2kmm-1-661F5051-32 2024-04-17 04:30:09.943872918 +0000 UTC m=+368943.344135620 Received: from herokuapp.com (unknown) by geopod-ismtpd-17 (SG) with ESMTP id An3RrJKvSZCtP1_MkIjxNw for ; Wed, 17 Apr 2024 04:30:09.869 +0000 (UTC) Date: Wed, 17 Apr 2024 04:30:09 +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: 94140 X-SG-EID: =?us-ascii?Q?u001=2E5PtzXJ23KrYzgM1nrOIr+EQ222PyrDaWSg0Er8CZ8tP86xyXmBM81zBKD?= =?us-ascii?Q?HreavdFYMbHjxXOR6UPMkt=2Fu9CyBIp6y52n8D2y?= =?us-ascii?Q?qA9zqurrgUc8Ch2nwGFJNHIgTUJkItpnXtZF5N8?= =?us-ascii?Q?qUSUxBpAyVsgyeRdtrP3BiRMrJYzcnxs1NidUKn?= =?us-ascii?Q?c+PGwS1L6WUSNPJsuuiyCQf0F48VcueqrMz2YbP?= =?us-ascii?Q?kb7ypgt8QD5gAJZiaS4wYwI7rCAsJgffXO4HLfD?= =?us-ascii?Q?wXxTZfq8rH=2FjcG1yzCsZwt5mKg=3D=3D?= To: ruby-core@ml.ruby-lang.org X-Entity-ID: u001.I8uzylDtAfgbeCOeLBYDww== Message-ID-Hash: OYFYKC6DHC3BBXC5EUIWYX3QIGRUIEUT X-Message-ID-Hash: OYFYKC6DHC3BBXC5EUIWYX3QIGRUIEUT 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:117545] [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). AMomchilov (Alexander Momchilov) wrote in #note-21: > nobu (Nobuyoshi Nakada) wrote in #note-17: > > I want `ENV.exchange_value` rather than `Hash#exchange_value`. > > Is there a reason to put it on `ENV`, but *not* on `Hash`? That seems like a needless restriction to me. `ENV` is a hash-like object, so I'm for `Hash#exchange` too. ---------------------------------------- Feature #20300: Hash: set value and get pre-existing value in one call https://bugs.ruby-lang.org/issues/20300#change-107938 * 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/