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Re: shift and logical or

by Kenosis (Priest)
on Nov 16, 2012 at 23:19 UTC ( #1004266=note: print w/replies, xml ) Need Help??


in reply to shift and logical or

Consider the following:

use strict; use warnings; printSomething('Hello, world.'); printSomething(); sub printSomething { my $string = shift || 'Nothing was sent.'; print $string, "\n"; }

First output:

Hello, world.

Second output:

Nothing was sent.

In subroutines, shift takes the first element off @_. In the case above, $string is initialized with whatever is sent to the subroutine. However, if nothing is sent, $string is initialized with 'Nothing was sent.' This is because of the logical or operation in Perl. If the first disjunct (shift) evaluates to true, then Perl stops there, since the overall express is true. However if the first disjunct evaluates to false (nothing to shift), Perl moves to the second disjunct. Thus, printSomething() prints Nothing was sent. Here's another way to 'say' this: the variable $string equals either what was sent to the subroutine or the string 'Nothing was sent.'

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[MidLifeXis]: Whew - you just saved the free world. <o)
[GotToBTru]: i guess it's a placeholder, the code will only fill it in if there is nothing else to use
[GotToBTru]: but then .. if you have nothing to say, why not say nothing?
[MidLifeXis]: I have a user who has a lot of say on how some of our processes work that abhors significant blanks. Perhaps that is a part of it. A not-so-obvious "this space intentionally left blank" indicator.
[MidLifeXis]: On the back end, however, that doesn't mean that i have to use that value to indicate "undefined", no matter how much he thinks I should.

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