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 [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 4F15B1F461 for ; Tue, 27 Feb 2024 16:47:06 +0000 (UTC) Received: from nue.mailmanlists.eu (localhost [127.0.0.1]) by nue.mailmanlists.eu (Postfix) with ESMTP id 510527EFAF; Tue, 27 Feb 2024 16:47:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ml.ruby-lang.org; s=mail; t=1709052420; bh=5X7LBZ5eKccFRGdikChXoaqCJR0MMoR7H37fMESjlX8=; 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=Esp6JhzKMi4sqX2iLtV9H0pZCgQiCBj2NJwtf8i8GXBVMT7DnZGApbOfcVQfGfncu Q35fNydmFPNk+ED9uCgulBOJv+/b9MowHMr5jVDhktc5V3huJWRGyYy17tvbFApjZH KSUoWTAOBdFgW5zWBRD+HmtHfHWNlrFDjdw1EiXQ= Received: from s.wrqvtbkv.outbound-mail.sendgrid.net (s.wrqvtbkv.outbound-mail.sendgrid.net [149.72.123.24]) by nue.mailmanlists.eu (Postfix) with ESMTPS id 32B6F7EFAA for ; Tue, 27 Feb 2024 16:46:57 +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=g+/Bz38I; 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=sLHVM29J2JaOBftshAOGHgU6bBebpFaYgSB1Wqnp/mQ=; b=g+/Bz38I270siZ7GC1pjqpSqCU4dqsuBqVI3B8V60mL6vuQh0sMt37FMv4CzGgU7ByAQ Rv9BtaU0fzW9UDo+UC/XYbX37lXKMt93aFJ+mW7dvW0N5w4qt7r/F6Zwx4mykhNOOpmKqp J+FKPZopl6rbdmmJ+7jXf7+3mbBkQ5OPKQEtuXmKAngW5Joj8tP7V6EZ8mw2atFx0ySN74 BjWpanmDkXdEweKiJNiNAD6Aek1FEIvQjdIvuSwcyHxcfMJqsqMBK2msHLU+pbGr340Hpv Ojm+wx94Ukbm1LU7AgpddXgCu8GxFgszjhb0DmC6RuecXAAAB6++IN1o489e4xJw== Received: by recvd-canary-6fb7cbf6c9-8qqrz with SMTP id recvd-canary-6fb7cbf6c9-8qqrz-1-65DE11FF-E 2024-02-27 16:46:55.694245913 +0000 UTC m=+419533.018115255 Received: from herokuapp.com (unknown) by geopod-ismtpd-31 (SG) with ESMTP id 6BxW3-4iTh6TLNAh-o-woA for ; Tue, 27 Feb 2024 16:46:55.681 +0000 (UTC) Date: Tue, 27 Feb 2024 16:46:55 +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: AMomchilov 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: 93531 X-SG-EID: =?us-ascii?Q?TXH2usWcWp=2FzFcOxYN6Di8zjS0LJPVcRDxMs1qy9L7d4+k8AQ49BDHpIjwSVMz?= =?us-ascii?Q?9YntVpiMPH+tfADRBOhubj+a4G1rD7MQwpbBSUi?= =?us-ascii?Q?RNRHcE3pvMDWytzYqhc5qTzMEF2XkJnmpJwTWix?= =?us-ascii?Q?856L7q0PlzZkaPOCPt0gn7bI0x+JDbpFL=2FMNL6r?= =?us-ascii?Q?MrYFLXf287z1ZmRfAPjT6iSkGvj9RJcDY3XqmQ6?= =?us-ascii?Q?gFBS5j7TvBXxDS8AmJDfqRqD0sIqjpU0J7UGSPG?= =?us-ascii?Q?H21jx6QP8aveEzQ25czymd1J+wMTCPt2TAU+47h?= =?us-ascii?Q?C+E=3D?= To: ruby-core@ml.ruby-lang.org X-Entity-ID: b/2+PoftWZ6GuOu3b0IycA== Message-ID-Hash: W4W7K6RSDVDWPPPUCMWDBMJACG7757GU X-Message-ID-Hash: W4W7K6RSDVDWPPPUCMWDBMJACG7757GU 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:116975] [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: "AMomchilov (Alexander Momchilov) via ruby-core" Cc: "AMomchilov (Alexander Momchilov)" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Issue #20300 has been updated by AMomchilov (Alexander Momchilov). @matheusrich I like that name in general, but it's really similar to the existing [`Hash#store`](https://ruby-doc.org/3.3.0/Hash.html#method-i-store) and the distinction is non-obvious. Swift calls this [`updateValue(_:forKey:)`](https://developer.apple.com/documentation/swift/dictionary/updatevalue(_:forkey:)), which returns a `Value?` ("the value that was replaced, or `nil` if a new key-value pair was added."), but it has a similar problem. I think `#exchange_value` is the best recommendation yet, because it makes it reasonably easy to guess what the return value would be, even without reading the docs. ---------------------------------------- Feature #20300: Hash: set value and get pre-existing value in one call https://bugs.ruby-lang.org/issues/20300#change-107022 * 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#update_value`, which has semantics are similar to this Ruby snippet: ```ruby class Hash # Exact method name TBD. def update_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.update_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/