CODEWITHSUNDEEP
perlvariablesscope
vts
vts

Reputation: 911

perl: can't get the global var before the place that var is defined

for example:

#!/usr/bin/perl
use Data::Dumper;

main();

my %h = (
    name => 'abc',
    value => '123',
);

sub main {
    print "Dumping the hash...\n";
    print Dumper(%h);
}

1;

the result is:

Dumping the hash...

So perl can call main before it be implemented, why it doesn't know the global var %h which even define early than main()?

Upvotes: 0

Views: 35

Answers (2)

ikegami
ikegami

Reputation: 385789

The my and the = are unrelated. In CS jargon, %h is actually defined before main is called (my). You're asking why the assignment wasn't performed (=).

main() is executed before the assignment to %h because main() is found before the assignment to %h in the code.

It's exactly the same reason that

print("abc\n");
print("def\n");

will never print

def
abc

Upvotes: 2

choroba
choroba

Reputation: 241858

There are basically two phases of processing of every Perl program: the compilation phase and the run phase. During the compilation phase, my and sub are processed, so Perl now knows you'll be using the globally accessible lexical variable %h. It's not populated, though - that would happen during the run phase. But, main is called before %h is populated.

Upvotes: 2

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