I would like to use $a
and $b
variables in my anonimous binary functions like it is done in sort {$a <=> $b} (1, 2, 3)
but I can not figure out why code like
#!/usr/bin/env perl
use strict;
use warnings;
Foo::Bar(sub { $a + $b });
package Foo;
sub Bar {
my ($function) = @_;
for my $i (1, 2, 3) {
local ($a, $b) = ($i, $i);
print $function->() . "\n";
}
}
does not work. While
#!/usr/bin/env perl
use strict;
use warnings;
Foo::Bar(sub { $_ });
package Foo;
sub Bar {
my ($function) = @_;
for my $i (1, 2, 3) {
local $_ = $i;
print $function->() . "\n";
}
}
works fine.
What am I doing wrong?
Passing Arguments to a Subroutine You can pass various arguments to a subroutine like you do in any other programming language and they can be acessed inside the function using the special array @_. Thus the first argument to the function is in $_[0], the second is in $_[1], and so on.
If you have subroutines defined in another file, you can load them in your program by using the use , do or require statement. A Perl subroutine can be generated at run-time by using the eval() function. You can call a subroutine directly or indirectly via a reference, a variable or an object.
$a
and $b
are special package variables. You're calling Foo::Bar
from within your main
package, so you need to set $main::a
and $main::b
to get it to work. You can use caller
to get the name of the calling package. This should work:
#!/usr/bin/env perl
use strict;
use warnings;
Foo::Bar(sub { $a + $b });
package Foo;
sub Bar {
my ($function) = @_;
my $pkg = caller;
for my $i (1, 2, 3) {
no strict 'refs';
local *{ $pkg . '::a' } = \$i;
local *{ $pkg . '::b' } = \$i;
print $function->() . "\n";
}
}
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