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 31AC31F44D for ; Thu, 14 Mar 2024 10:13:03 +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=diz9Qken; 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=b4qxMZaQ; dkim-atps=neutral Received: from nue.mailmanlists.eu (localhost [127.0.0.1]) by nue.mailmanlists.eu (Postfix) with ESMTP id A44B98337D; Thu, 14 Mar 2024 10:12:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ml.ruby-lang.org; s=mail; t=1710411175; bh=S7XX3NcDrG95NPvL2X+laQeFvMeAZwo2yLoZJSqgmr4=; 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=diz9QkenyGFj+k5XejhfLtbOy9jsq3lqaIMK71lRXrYtLnUdIvkd7xLsukg+Z1Yk/ /uD4I2x+EGzbx+D7S8ql/qyQLEEutKPlLshljKPmV4mWVb2FrGLg2qqNvC/FqXJTjL U1pzxQDEi2+KIrurrtcS0sZ2PfZyw+u5OOhx1M5c= Received: from s.wfbtzhsw.outbound-mail.sendgrid.net (s.wfbtzhsw.outbound-mail.sendgrid.net [159.183.224.105]) by nue.mailmanlists.eu (Postfix) with ESMTPS id 3A19B8335B for ; Thu, 14 Mar 2024 10:12:52 +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=b4qxMZaQ; 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=UKbdWop11OOVPNVzQqlmZSiuatysjUDYfvF6v67eZs8=; b=b4qxMZaQcsIKumhDjXKu9B8273V4sovgxph5ykvWmt3SN24c6A99Zi1yDn7XArh9wJAg zC8CImUFP2Hr5Sd7eVUqLtrXrzvzxXDEfcK7PZifz1u4AJu7tfDZFn+SpupU6QohGvF6fA 5Uvl8+Tq5OQjGT409IPeGGmTPiWc13iusLe1aHASIqCW3BAHggNmz/iDbvcZvBeO8k8wXr KM9sMCB6nFdd3XatR+aMbFrYIxF5rVvtD9rKGoVSgHj8aK5BbG51QcqLJ0NsqreC8RinQO mlUOVWwWdFqcHTT5kyuMChE99gfxG7f1gIsvTtxart1buJZH0rgOOAjWmNlh68bg== Received: by filterdrecv-6b965fd7fb-qj65c with SMTP id filterdrecv-6b965fd7fb-qj65c-1-65F2CDA3-3 2024-03-14 10:12:51.258697301 +0000 UTC m=+818287.803082996 Received: from herokuapp.com (unknown) by geopod-ismtpd-35 (SG) with ESMTP id 9MpuPnN8TtGTb_eUi_vNtw for ; Thu, 14 Mar 2024 10:12:51.122 +0000 (UTC) Date: Thu, 14 Mar 2024 10:12:51 +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: mame 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: 93722 X-SG-EID: =?us-ascii?Q?u001=2Ep+ckLDtT+4Y5c+H0YCkEnsuWiCQmn3OZA=2F9FzjoR6ZZlPaMv54M7EFoSM?= =?us-ascii?Q?CX5Trc79ep2R5F+0oYS4n23jq1cv8epVYdS5mvn?= =?us-ascii?Q?HO2T+Dgtbq5jZwSSE4dhU0LRhTANVGyzNDcXaXs?= =?us-ascii?Q?0RlL51iqC3a9NUO+ZIZhV8JWDx3DSkv3VwEim8r?= =?us-ascii?Q?6ftpymNOjkEKA5f=2Fp82xZgeqtNL7Mqpg31d51Xk?= =?us-ascii?Q?CTfqEdehei2owAnnWN89MmmAmGduah99RMEPLCy?= =?us-ascii?Q?QTO7gFvc3jLJJZslNu=2F7fpu0Zg=3D=3D?= To: ruby-core@ml.ruby-lang.org X-Entity-ID: u001.I8uzylDtAfgbeCOeLBYDww== Message-ID-Hash: PZVG5X63HYMN6R24ZDDW3BXJHF6YU7DQ X-Message-ID-Hash: PZVG5X63HYMN6R24ZDDW3BXJHF6YU7DQ 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:117156] [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: "mame (Yusuke Endoh) via ruby-core" Cc: "mame (Yusuke Endoh)" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Issue #20300 has been updated by mame (Yusuke Endoh). Discussed at developers meeting. @shyouhei pointed out that `Set#add?` could be improved with a single lookup by looking at the change in size, without this proposal. https://bugs.ruby-lang.org/issues/20301#note-8 @matz said that we need another good use case to introduce this if it is sufficient for `Set#add?`. ---------------------------------------- Feature #20300: Hash: set value and get pre-existing value in one call https://bugs.ruby-lang.org/issues/20300#change-107243 * 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/