in reply to Re: (tye)Re: Functions
in thread Functions

exit main( @ARGV );
{
    my $sub;
    BEGIN {
        $sub= sub {
            # ...
        };
    }
    sub GlobalRoutine {
        &$sub( ... );
    }
}
sub main {
    # ...
}

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It is easy to put this in places where the BEGIN block becomes necessary. Some are much more subtle than this. Without the BEGIN block, $sub is declared and GlobalRoutine is compiled before $sub is initialized so it then becomes possible for GlobalRoutine to be called while $sub is still undef.

I'm sorry that Perl doesn't have real static variables such that I have to resort to an extra empty block and doing the initialization in a BEGIN block. Note that this trick won't work if you are using mod_perl.

FYI, since I didn't use any local variables in the anonymous subroutine, it isn't a closure in my book.

        - tye (but my friends call me "Tye")

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Re: (tye)Re2: Functions
by fgcr (Novice) on Jan 30, 2001 at 02:25 UTC
    Thank you. This has helped a lot.
[reply]
Re: (tye)Re2: Functions
by KM (Priest) on Jan 30, 2001 at 01:45 UTC
    It works fine from my tests without the BEGIN block since $sub is initialized befor the compiler will get to GlobalRoutine.

    Since $sub goes out of scope, but there is still a pointer to it which can only be accessed via GlobalRoutine, I would consider it a closure, although possibly not by the true sense of the definition. However, $sub could itself use lexical, and meet the 'definition'. I'll call it a pseudo-closure, you can call it a 'closing' if you like.

    Cheers,
    KM

[reply]

      It works fine from my tests without the BEGIN block since $sub is initialized before the compiler will get to GlobalRoutine.

      Then I guess you missed my addition last time. Here: 

      #!/usr/bin/perl -w
use strict;

exit main( @ARGV );

{
    my $sub;
    ## BEGIN {
        $sub= sub {
            warn "Called local sub: @_\n";
        };
    ## }
    sub GlobalRoutine {
        &$sub( "Test" );
    }
}

sub main {
    GlobalRoutine("hi");
    return 0;
}
__END__
This produces the following:
Use of uninitialized value in subroutine entry at localsub.pl line 14.
Can't use string ("") as a subroutine ref while "strict refs" in use a
+t localsub.pl line 14.

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              - tye (but my friends call me "Tye")
[reply]
[d/l]
        Yes? So you move the call to main below the block and you still don't need it in a BEGIN. You would squash a normal closure by doing this as well. The BEGIN isn't needed unless you design your script so it is. 

        #!/usr/bin/perl -w

use strict;
use vars qw($sub);

#exit main(); # Useless use of closure below if called like this
          # BEGIN block would be needed in this case.

{
    my $time = time();
    $sub = sub {time - $time};
}

exit main(); # No problem, no BEGIN needed.
sub main {
    print &$sub;
    sleep 2;
    print &$sub;
    return 0;
}

        [download]

        Cheers,
        KM

[reply]
[d/l]

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