On 07/02/2012 07:20 PM, Bruno Haible wrote: > Hi Eric, > > How can we fix this? > > I'm thinking about two macros AC_DEFUN_ONCE_IFNEEDED, AC_REQUIRE_IFNEEDED
Again, avoiding the AC_ namespace unless Autoconf 2.80 adds this methods
might be wise, we'd be safer with the names gl_DEFUN_ONCE_IFNEEDED and
gl_REQUIRE_IFNEEDED.
> that will operate like AC_DEFUN_ONCE and AC_REQUIRE except that they will
> ensure that the body is executed only when actually needed.
>
> AC_DEFUN_ONCE_IFNEEDED would use shell functions, roughly like this:
>
> AC_DEFUN_ONCE_IFNEEDED([FOO], [
> AC_REQUIRE([DEPENDENCY1])
> AC_REQUIRE_IFNEEDED([DEPENDENCY2])
> BODY-CODE
> ])
>
> =>
>
> AC_DEFUN([FOO],
> [
> AC_REQUIRE([FOO_BODY])
> foo_func
> ])
> AC_DEFUN([FOO_BODY], [
> AC_REQUIRE([DEPENDENCY1])
> AC_REQUIRE([DEPENDENCY2])
> foo_var=false
> foo_func ()
> {
> if ! $foo_var; then
> dependency2_func
> BODY-CODE
> foo_var=true
> fi
> }
> ])
>
> Eric, is it possible to write such macros? It is complicated, sure. But
> is there something that makes the idea unimplementable?
Yes, I think such an implementation should be possible. Doing it using
only the constructs available in autoconf 2.59 will be a bit
interesting, but I can certainly help out.
It might even be shorter to do:
AC_DEFUN([FOO_BODY], [
AC_REQUIRE([DEPENDENCY1])
AC_REQUIRE([DEPENDENCY2])
foo_func ()
{
foo_func() { :; }
dependency2_func
BODY-CODE
}
])
to use self-redefining shell functions instead of having to use both a
shell function and a witness variable.
--
Eric Blake ebl...@redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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