CODEWITHSUNDEEP
perl
kurotsuki
kurotsuki

Reputation: 4777

What is this line of code trying to do?

This Perl code is part of the variable declaration at the beginning of a piece of code. What does it mean?

my $EXPLICIT_YEAR = $ALL_PAGES ? 0 : ($store{year} || $current_year);

Upvotes: 0

Views: 171

Answers (5)

user78706
user78706

Reputation:

I know 0 perl but a lot of C, so taking a guess here: 

  Set variable EXPLICIT_YEAR to  
     (  if ALL_PAGES == true then 0  
        else ( (get store indexed at year) or current_year ))

The or operation is 

false or false = false  
false or true  = true
true  or false = true  
true  or true  = true

Upvotes: 0

TLP
TLP

Reputation: 67900

my $EXPLICIT_YEAR = $ALL_PAGES ? 0 : ($store{year} || $current_year);

This expression is using the Ternary "?:" operator, combined with a subexpression using the || C-style logical OR. See perldoc perlop.

$ALL_PAGES ?

The expression before the ? - the condition - is evaluated as a boolean expression. A true value meaning any value that is not zero, the empty string or undefined (not declared). 

0 : ( $store{year} || $current_year )

The values on either side of : are the values to be returned, depending on the return value of the condition. If the condition evaluates true, return the leftmost value, otherwise the rightmost. The leftmost value is simply zero 0.

$store{year} || $current_year

The rightmost value is an expression itself, using the C-style logical OR operator. It will return the leftmost value, if it evaluates true (and ignore the rightmost). Otherwise it will return the rightmost value. So:

  • if $ALL_PAGES is true, then set $EXPLICIT_YEAR to zero
  • else if $ALL_PAGES is false, then:
  • if $store{year} is true, then set $EXPLICIT_YEAR to $store{year}
  • else set $EXPLICIT_YEAR to $current_year

Upvotes: 1

kbenson
kbenson

Reputation: 1464

It's equivalent to this:

my $EXPLICIT_YEAR;
if ($ALL_PAGES) {
    $EXPLICIT_YEAR = 0;
}
else {
    # $EXPLICIT_YEAR = $store{year} || $current_year;
    if ($store{year}) {
        $EXPLICIT_YEAR = $store{year};
    }
    else {
        $EXPLICIT_YEAR = $current_year;
    }
}

The $conditional ? $true : $false portion is a ternary if. The $store{year} || $current_year portion uses the fact that the || operator returns the first value that evaluates to true, allowing $current_year to be used if $store{year} is "false" (zero, empty string, etc.)

Upvotes: 4

dom
dom

Reputation: 651

i think thats a way of doing a if/then/else see here: http://www.tutorialspoint.com/perl/perl_conditions.htm

Upvotes: 0

airplaneman19
airplaneman19

Reputation: 1159

I'm not a Perl developer, but I'm 99% sure (this holds in most other languages) that it equates to this: If the variable $ALL_PAGES is true (or 1), then 0 is evaluated, and if not, ($store{year} || $current_year) is evaluated.

Upvotes: 0

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