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Re: (require 'cus-load) clobbers match-data

From: Glenn Morris
Subject: Re: (require 'cus-load) clobbers match-data
Date: Tue, 16 Feb 2010 15:13:40 -0500
User-agent: Gnus (www.gnus.org), GNU Emacs (www.gnu.org/software/emacs/)

Geoff Gole wrote:

> While trying to puzzle out bug 5533
> <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=5533>, I've found that
> (require 'cus-load) will stomp on match data if the file is not
> already loaded:

I'm not sure that 5533 can reasonably be classed as a bug. It seems a
strange way to do a search-replace - what's wrong with M-x query-replace?

In general, there should be no expectation that any operation in Emacs
will preserve the match-data (unless it explicitly says so).

> Maybe require should save and restore the match data itself?

This would be completely unnecessary in the vast majority of cases.
Since a require can run arbitrary code, there should be no expectation
that it preserves match-data.

The usual answer to "why doesn't FOO preserve the match-data" is "the
code calling FOO should take care to preserve the match-data if it
cares about it", rather than "FOO should always preserve the

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