-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 According to Paolo Bonzini on 1/23/2009 5:25 AM: >>> It's too late for doing that: AC_DEFUN_ONCE was introduced on 2004-10-11. >> I know. >> >>> Besides that, AC_DEFUN_ONCE and AC_DEFUN_IDEMPOTENT have really opposite >>> semantics. You cannot confuse people more than by using the same name for >>> two entities with opposite semantics. >> It looks to me like, in the wild, AC_DEFUN_ONCE is used for idempotent >> macros (and in Autoconf too, see AC_CANONICAL_*). The only correct use >> of AC_DEFUN_ONCE (where the warning *is* desired) is AC_NO_EXECUTABLES; >> and not even fully correct, as you'd want an error there.
And you can still achieve an error for that case, by writing a self-modifying macro: AC_DEFUN([AC_NO_EXECUTABLES], [first-time defn... m4_define([AC_NO_EXECUTABLES], [m4_fatal(...)])]) > > Besides, what's the difference between expanding once only a macro, or > expanding once only a macro + give a warning? > > m4_define([m4_defun_once], [dnl > m4_defun([_$0_$1], [$2])dnl > m4_defun([$1], [m4_require([_$0_$1])]) I like this idea. I agree that this proposed definition of AC_DEFUN_ONCE is sufficient for our needs - it guarantees that a macro is expanded exactly once, and that the real body is required (and thus hoisted). The use of AC_DEFUN_ONCE is to guarantee that the macro body is expanded exactly once. The old semantics merely warned the user if a second expansion was encountered, but the new semantics guarantee that any second expansion is a no-op; either way, the end result is a single expansion. And by making the new definition call m4_require under the hood (plus whatever magic to avoid a warning), we have guaranteed that no out-of-order expansion happens. Plus, it will be easy to make gnulib-common.m4 provide an override of AC_DEFUN_ONCE that works in this manner even with older autoconf. Thus, I don't think we need AC_DEFUN_IDEMPOTENT; rather, we just make AC_DEFUN_ONCE the single macro that is the user's way to declare that a macro body is only needed once. I'll work up patches for both the autoconf and gnulib side of things. - -- Don't work too hard, make some time for fun as well! Eric Blake e...@byu.net -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (Cygwin) Comment: Public key at home.comcast.net/~ericblake/eblake.gpg Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkl55KcACgkQ84KuGfSFAYCRNwCfTacwi6j66kwSN44QKgJ3Z/ro 1RIAnAzUMUV4vAj4NG0w7+AGIHI95uL5 =AYp2 -----END PGP SIGNATURE-----
