While that code snippet is correct, the first paragraph of explanation is actually partially wrong.

.... it creates a kind of global variable with restricted scope! If this is in a subroutine, the second time you call the sub, you get exactly the same array, not a new one.

This is not true. Look at the following: 

use strict;
use warnings;
sub mytest {
    my $var if 0;
    $var++;
    print $var, "\n";
}
mytest();
mytest();
__OUTPUT__
1
1

[download]

We see several important things in that snippet. First, there are NO errors under strictures, and no warnings. Second, $var is NOT the same variable each time mytest() is called. If we had created a closure, the output would have been 1 and 2, not 1 and 1. If we had autovivified a global, we would have gotten a strictures error, or at minimum, the output would have been 1 and 2. But none of that happens. We get a new lexical variable each time mysub() is called.

Why?

Because my has two elements to how it works. First, the compiletime side. At compiletime, the framework is made for a lexical variable. Yet at compiletime, it is too soon to know the outcome of program logic. So the lexical is created without any regard for logic; all that matters is lexical scope.

At runtime, logic springs to life. And if the "my" declaration has an assignment component to it, as in  my $x = 10 if $condition; that assignment will only take place if $condition is true. But $x exists within the lexical block whether or not $condition is ever true. And it falls out of scope just like any good lexical would, when the lexical block ends, even if its a subroutine.


Dave

In reply to Re: Re: declaring same variable by davido
in thread declaring same variable by samy1212

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