From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Mattias =?UTF-8?Q?Engdeg=C3=A5rd?= Newsgroups: gmane.emacs.bugs Subject: bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations? 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Thu, 9 Jul 2020 10:20:46 +0000 In-Reply-To: X-Mailer: Apple Mail (2.3445.104.14) X-CTCH-RefID: str=0001.0A782F17.5F06EF81.0064, ss=1, re=0.000, recu=0.000, reip=0.000, cl=1, cld=1, fgs=0 X-CTCH-VOD: Unknown X-CTCH-Spam: Unknown X-CTCH-Score: 0.000 X-CTCH-Flags: 0 X-CTCH-ScoreCust: 0.000 X-CSC: 0 X-CHA: v=2.3 cv=A5MSwJeG c=1 sm=1 tr=0 a=SF+I6pRkHZhrawxbOkkvaA==:117 a=SF+I6pRkHZhrawxbOkkvaA==:17 a=kj9zAlcOel0A:10 a=M51BFTxLslgA:10 a=oX08kPI8AAAA:8 a=yJ4EgYy2VQUyobU5FV4A:9 a=fVpxQXZP2W1u2YHm:21 a=HyK-AmsYuPH8IRny:21 a=CjuIK1q_8ugA:10 a=HoS0eNqkKlFy34tK5QRU:22 X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "bug-gnu-emacs" Xref: news.gmane.io gmane.emacs.bugs:182860 Archived-At: 9 juli 2020 kl. 00.19 skrev Andrea Corallo : > Or is it maybe that the only way to certainly have a mutable string is > with `copy-sequence' or `make-string'? Yes; since the need for a mutable value is very unlikely, creating a = fresh copy every time just in case would be a big waste of resources. = Otherwise, we could only 'optimise' (concat "abc" "def") to (copy-sequence "abcdef") which would be a very modest improvement, for very little gain. The two functions you mentioned are indeed guaranteed to return fresh, = mutable strings and thus cannot be marked 'pure'. String mutation is something of a special case: it is rare, yet its mere = possibility incurs costs even for code that doesn't use it. Better try = to keep that cost to a minimum.