Hello, On 2/21/17, Reuben Thomas <r...@sc3d.org> wrote: > In the first example for AC_ARG_WITH, there's an "if test…fi" block: > > if test "x$with_readline" != xcheck; then > AC_MSG_FAILURE( > [--with-readline was given, but test for readline failed]) > fi > > Is there some reason why this doesn't use AS_IF?
Probably the author simply preferred regular shell if statements. There's nothing wrong with a plain 'if' here, so the author used it. The main practical difference between AS_IF and regular 'if' relates to the AC_REQUIRE machinery. Since Autoconf "understands" the AS_IF macro, it can hoist AC_REQUIREd or AC_DEFUN_ONCE macros expanded inside the if body outside of the condition (this is normally the desired result). I would not expect AC_MSG_FAILURE to use such expansions so regular 'if' is fine. Moreover, this particular 'if' is found inside the body of AS_IF so the hoisting should work anyway. > I see a comment above saying: > > @c FIXME: Remove AS_IF when the problem of AC_REQUIRE within `if' is > solved. > > but it's not clear whether that's relevant (the commit log that introduced > the comment doesn't seem to explain it). Just speculating, but the original author in 2005 probably did not like AS_IF stylistically and was hoping that, someday, AC_REQUIRE would work with regular shell 'if' statements. Then the examples could be reworked to not use AS_IF. I expect such magic will probably never happen so AS_IF is here to stay. Cheers, Nick
