if only blocks were avoidable...

[yosefm]

Or are they? I'm trying to write a module that uses bytes.pm only if it was requested in the import list, like - use module qw(LegacyEncoding and other options);

The problem is that if I use if, bytes will only be scoped to the if block. And anyway if I manage to avoid that (like with $legacy and use bytes) it will still be scped to the import sub.

Any way around it?
Thanks.

[liz]

The use bytes is basically setting $^H at compile time.

According to that documentation, you should be able to do:

BEGIN { require bytes; bytes->import if $condition }

inside the block where you want the use bytes to be conditionally set. Of course, if you don't put it in a block, the file in which the source sits, will be your scope.

This seems the right thing according to the docs and seems to work with stricture:

$foo = $a;
BEGIN { require strict; strict->import if 1 }
$foo = $a;
__END__
Variable "$foo" is not imported at x line 3.
Global symbol "$foo" requires explicit package name at x line 3.
x had compilation errors.

If the import is not done, this runs without any errors:

$foo = $a;
BEGIN { require strict; strict->import if 0 }
$foo = $a;
__END__

Hope this made sense and helps.

Liz

[yosefm]

OK, it turns out that this isn't what I need, because if I use BEGIN, I can't use parameters passed to sub in order to decide on the condition. I can only use environment variables, perl variables and other stuff that already exists before anything happens.

What I need is this:

sub import {
    $_[1] eq 'StoneAge' and use bytes globally; #no such thing.
}

BEGIN can't achieve that.

[liz]

Ok, I guess I missed that particular point. Well, I think it is possible, but it's rather yucky and it suffers from the same problems that AutoLoader and the likes have. Basically, you compile your code in a two step process. First to compile the "import" routine. Then, when the import routine is called, the rest of the source is compiled Consider module Foo:

package Foo;
require bytes; # make sure the module is loaded without (un)import

$bytes = 0;    # flag: whether bytes should be enforced
$evalled = 0;  # flag: whether rest of source has been compiled

sub import {
    unless ($evalled++) {               # we haven't evalled the rest 
+before
        $bytes = ($_[1] eq "usebytes"); # should bytes be enforced?
        local $/;                       # enable slurp mode
        eval <DATA>;                    # compile rest of source (afte
+r __DATA__)
        die $@ if $@;                   # die now if an error occurred
    }
};
1;                              # in order for require of Foo.pm to be
+ successful
__DATA__                        # actual source of module starts here
BEGIN {bytes->import if $bytes} # activate bytes if flag set
sub new { bless {},shift }      # example routine

Then, in an example program, you would do:

use Foo 'usebytes'; # or something else to not use bytes
my $foo = Foo->new;

Hope this will help you in your quest.

Liz

[yosefm]

So if I understand what you (and perlvar) say correctly, the BEGIN block is what's going to make my import globally scoped? If that's the case then I guess that's what I was looking for.
Thanks.

[Anonymous Monk]

No. Wrapping an import call in a BEGIN block will make it happen at compile time.

[jeffa]

Not quite sure if i am following you, but have you tried require instead? The "problem" with use is that no matter where it is, the module will be loaded. Consider this:

if (0) {
   use CGI qw(:standard);
}

print header,"\n";

Which does load CGI.pm and no compile error happens because there really is a header() method available. Try using require instead.

jeffa

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