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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, T_SCC_BODY_TEXT_LINE autolearn=ham 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)) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id 097821F44D for ; Mon, 26 Feb 2024 10:16:36 +0000 (UTC) Received: from nue.mailmanlists.eu (localhost [127.0.0.1]) by nue.mailmanlists.eu (Postfix) with ESMTP id 5319382C12; Mon, 26 Feb 2024 10:16:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ml.ruby-lang.org; s=mail; t=1708942588; bh=9LpOK9u355Z1M5gw+WEIyrQDNKlTlyFPF+RHEFYlYm4=; 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=wQaDFrpglJ67EU3m2kjS867NApb22xMY0dtNopfs6OSJzDLWTXi/cskKqAYwyBrkt HASm1wFFIwrvGLUM0LFmL82N3Zq4LPGedrJgImlhhIkdXQ37jNZoE8gy2YbrkkULm9 ovlKnGLClJhz9twugUt9O7v/zb0IS7i2e1FXHVXg= Received: from s.wrqvwxzv.outbound-mail.sendgrid.net (s.wrqvwxzv.outbound-mail.sendgrid.net [149.72.154.232]) by nue.mailmanlists.eu (Postfix) with ESMTPS id BE0EF82A80 for ; Mon, 26 Feb 2024 10:16:23 +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=hAhRvutp; 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=JS0KQ7hwgwuz+/UsBsoYa0zOzFe2cP1PFe4lW/RdAic=; b=hAhRvutpbyXQki00pWRJico4dIbkIenZBWAkw+3yAuqybfG2xmDSqjtHyrQ/P1fjwDJi 8wiZk23lQA4AfyeB2OJfuNlzdlhtExDUFVJEZQmGJ++CVEUok+JBoye7f42IjpR+SMaS0O OC5WwselDZPmG8FAotb7yqfNo+FR5xGh/XyC9EFRNtywhTfvj1PejEVOQNcy0a/v+LhNFw yCsKJMShy3RWUaqZ2wUI2wjjeeX9f+BmuZVjUEbzs1gTmM1bHua5nvc3fypHJRvWBSQ9fU LX4wavUll0jlPBrW4ZppsHIZYZI+PZI2yKpnLcw0uupf6kwrD1aYTT1clq2xxqbQ== Received: by filterdrecv-655bd866f5-l7lp4 with SMTP id filterdrecv-655bd866f5-l7lp4-1-65DC64F5-31 2024-02-26 10:16:21.801513981 +0000 UTC m=+1519189.118317866 Received: from herokuapp.com (unknown) by geopod-ismtpd-19 (SG) with ESMTP id jltKm23ITCqxLUPJNeSDXw for ; Mon, 26 Feb 2024 10:16:21.717 +0000 (UTC) Date: Mon, 26 Feb 2024 10:16:21 +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: Eregon 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: 93503 X-SG-EID: =?us-ascii?Q?DvL3W2Xo+Vk=2FeUn3F50L=2FNc8u9NqZCnbE0mXZHiyye4R1YZg=2FtAFc0SAFzpcS=2F?= =?us-ascii?Q?Zcr7BqPN=2FYCcMZBMITNeIci9STxYay0JAJWPbek?= =?us-ascii?Q?rFR+qU=2Fs5OUvzNSOshvLRLZv8CB5LOHAcr0TBDC?= =?us-ascii?Q?WHZmZD7ODT1MsJsMBSJhbxUGfrKniFsnJjgvMfh?= =?us-ascii?Q?5EkBNOo4W7cFX3ncIByIDM6SmvJ4MNJtteZR6fK?= =?us-ascii?Q?VIPmfB6f0IIvxom9pZG+riggvv5jCLucfwRUFiZ?= =?us-ascii?Q?n++OdbJZa4pMAnGbsGx0A=3D=3D?= To: ruby-core@ml.ruby-lang.org X-Entity-ID: b/2+PoftWZ6GuOu3b0IycA== Message-ID-Hash: UGYPIAVJRVB6C6DP5BGUJQU5VHBC3LAE X-Message-ID-Hash: UGYPIAVJRVB6C6DP5BGUJQU5VHBC3LAE 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:116947] [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: "Eregon (Benoit Daloze) via ruby-core" Cc: "Eregon (Benoit Daloze)" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Issue #20300 has been updated by Eregon (Benoit Daloze). FWIW, concurrent-ruby calls this `get_and_set`: https://ruby-concurrency.github.io/concurrent-ruby/master/Concurrent/Map.html#get_and_set-instance_method `Hash#exchange_value` sounds fine to me too. ---------------------------------------- Feature #20300: Hash: set value and get pre-existing value in one call https://bugs.ruby-lang.org/issues/20300#change-106987 * 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/