GNU bug report logs - #78162
[PATCH] hash-table-contains-p: Avoid creating a symbol on every call

Previous Next

Full log

Message #26 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Rudolf Schlatte <rudi <at> constantly.at>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: bug#78162: [PATCH] hash-table-contains-p: Avoid creating a symbol
 on every call
Date: Sun, 11 May 2025 08:02:03 +0200

Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of
text editors" <bug-gnu-emacs <at> gnu.org> writes:

> [ Ideally, this function would be replaced with one which doesn't return
>   just `t` but an actual "handle" on the hash-table slot, so that we can
>   then access that slot without redoing the key lookup.  It would allow
>   doing thing like `push` or `incf` on a hash-table entry without
>   looking up the key twice.
>   But doing so without allocating an object is hard with the current
>   hash-table design (and would come with its own downsides).  ]

A micro-optimization could be for the hash table to remember the last
key lookup, so that something like this hits a fast path for the second
lookup of the same key:

(when (hash-table-contains-p key table)
  (push 'x (gethash table key)))
  

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.