RE: How do I disable modules in a script

[Wu, Gang (Steven)]

Hi, Eric,

Your method needs to have all the C code in the BEGIN block. What if I
have a rather long C code and I want it to be at the end of the file? Is
there any way?

Thanks!

Steven

-----Original Message-----
From: Eric Wilhelm [mailto:[EMAIL PROTECTED] 
Sent: Monday, March 22, 2004 8:11 PM
To: [EMAIL PROTECTED]
Subject: Re: How do I disable modules in a script

# The following was supposedly scribed by
# Sisyphus
# on Monday 22 March 2004 09:31 pm:

|use warnings;
|
|BEGIN {
|   eval{require Inline::C};
|   if($@) {
|     print "No Inline::C here\n";
|     # do whatever you want
|     exit;
|     }
|   }
|
|use Inline C => <<'EOC';
|
|void got_it() {
|      printf("We have Inline::C\n");
|      }
|
|EOC
|
|got_it();
|
|__END__
|
|Seems to work as you want. As it is it prints "We have Inline::C". If I
|change all occurrences of 'Inline::C' (and 'Inline C') to 'Inline::D'
|(and 'Inline D') then it prints "No Inline::D here" and quietly exits.

Sounds about right, except I think the OP wanted to do something besides
exit 
if Inline::C is not available.  Usually, you would have a require()
statement 
for this sort of thing, since those don't get caught at compile time
(trouble 
with use() is that the interpreter wil find it anywhere.)

This won't work:
  require Inline C => <<'EOC';

So, you would have to call the import routine directly:

BEGIN {
   eval{require Inline::C};
   if($@) {
     print "No Inline::C here\n";
     # do whatever you want
     exit;
     }
   else {
     Inline::import(Inline, C => <<'EOC'
     void got_it() {
        printf("we have inline::C\n");
     }

     EOC
     );
     }

   }



Example:  you've written a function (or class) in both C and Perl, and
the C 
one is faster, but you want the Pure Perl one to be available as a
fallback.

You could also put the 'use Inline C => $code' line inside of an eval,
or 
(maybe a better plan) write two modules and do an eval {require } on
each in 
turn.  The one which contains 'use Inline::C' will fail the require, so
you 
can fall-back on the pure-perl one in an else{} block.

Of course, as Rob has demonstrated, you need to do all of this fancy
stuff in 
a BEGIN block.

--Eric