Conditional function replacement

Thelonius has asked for the wisdom of the Perl Monks concerning the following question:

I want to create a function that will use the POSIX WEXITSTATUS function if it is defined, otherwise use a default function.
What I've come up with is this:

package Pexitstat;
require Exporter;
our @ISA = qw(Exporter);
our @EXPORT = qw(exitstatus);

our $WEXITSTATUS = sub { $_[0] >> 8 };
sub exitstatus {
  &$WEXITSTATUS($_[0]);
}
if (eval "use POSIX; 1") {
  local $! = 0;
  my $EAGAIN = POSIX::constant("EAGAIN", 0);
  my $val = POSIX::constant("WEXITSTATUS", 0);
  if ($! == $EAGAIN) {
    $WEXITSTATUS = sub { POSIX::constant("WEXITSTATUS", $_[0]) };
  }
}

1;
[download]

I also tried the slightly shorter:

package Pexitstat;
require Exporter;
our @ISA = qw(Exporter);
our @EXPORT = qw(exitstatus);

sub exitstatus {
  $_[0] >> 8;
}
if (eval "use POSIX; 1") {
  local $! = 0;
  my $EAGAIN = POSIX::constant("EAGAIN", 0);
  my $val = POSIX::constant("WEXITSTATUS", 0);
  if ($! == $EAGAIN) {
    *exitstatus = sub { POSIX::constant("WEXITSTATUS", $_[0]) };
  }
}

1;
[download]

which works, but gives the warning "Subroutine exitstatus redefined at Pexitstat.pm line 14."

Is there a better way to accomplish this?

Comment on Conditional function replacement Select or Download Code

Replies are listed 'Best First'.
Re: Conditional function replacement by shotgunefx (Parson) on Apr 16, 2002 at 19:40 UTC
undef &existstatus before the reassignment will silence the redefined warnings. -Lee "To be civilized is to deny one's nature."	[reply]
Re: Re: Conditional function replacement by Thelonius (Priest) on Apr 16, 2002 at 20:15 UTC
Thanks, that's just what I needed.	[reply]
Re: Conditional function replacement by Thelonius (Priest) on Apr 16, 2002 at 19:43 UTC
I've come up with a third variant, which I like, but still wondering if anybody knows of any drawbacks with this or a better way: `package Pexitstat; require Exporter; our @ISA = qw(Exporter); our @EXPORT = qw(exitstatus); my $EAGAIN; if (eval "use POSIX; 1" && ($EAGAIN = POSIX::constant("EAGAIN", 0)) && defined(POSIX::constant("WEXITSTATUS", 0)) && $! == $EAGAIN) { exitstatus = sub { POSIX::constant("WEXITSTATUS", $_[0]) }; } else { exitstatus = sub { $_[0] >> 8} } 1;` [download]	[reply] [d/l]