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Re^3: Perl array declaring

by BillKSmith (Chaplain)
on Jun 01, 2013 at 20:55 UTC ( #1036500=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Perl array declaring
in thread Perl array declaring

Variables can be declared as many times as you like...
True only for global variables, and even then, not without warnings. Change your 'our' to 'my' and your program no longer works. You are creating new variables with the same name. Warnings inform you that the new variable masks an earlier declaration.
Bill


Comment on Re^3: Perl array declaring
Re^4: Perl array declaring
by Laurent_R (Parson) on Jun 01, 2013 at 22:09 UTC

    Variables can be declared as many times as you like...

    True only for global variables, and even then, not without warnings. Change your 'our' to 'my' and your program no longer works. You are creating new variables with the same name. Warnings inform you that the new variable masks an earlier declaration.

    I surely understand what you meant to say and agree with what you intended to say, Bill, but lexical variables can indeed be declared as many times as you like, provided they are not declarred in the same lexical scope. For example, the following code declares the same lexical variable four times without any error or warning:

    use strict; use warnings; my $var = 1; { my $var = 2; print $var, "\n", } print "$var \n"; foreach my $var (1..5) { print $var, "\n"; } print double(7); sub double {my $var = shift; return 2 * $var;}

    and happily prints:

    $ perl scope.pl 2 1 1 2 3 4 5 14

    Which does not mean at all that I recommend doing that. It can be done, and is useful sometimes, but we should avoid leading to obfuscation.

      In Tobyink's example, there is only one global variable, $foo. Use of 'use warnings' would have warned about multiple declarations. Change every 'our' to 'my' and the warning changes to reflect new variables masking the old.

      In your case, you also have multiple variables with the same name, but in different scopes. As you said, this is sometimes useful, but you should not think of it as multiple declarations of the same variable.

      Bill

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