CODEWITHSUNDEEP
perl
photosynthesis
photosynthesis

Reputation: 2890

what does the double forward slash mean here?

I'm new to Perl and came across this piece of code at work, I search for a while but did not find the answer. Can anyone help to explain its function in plain english? thanks.

my $abc = delete $args{ 'abc' } // croak 'some information!';

Upvotes: 38

Views: 19828

Answers (2)

AntonH
AntonH

Reputation: 6437

From this page here: http://perldoc.perl.org/perlop.html#Logical-Defined-Or

Although it has no direct equivalent in C, Perl's // operator is related to its C-style or. In fact, it's exactly the same as ||, except that it tests the left hand side's definedness instead of its truth. Thus, EXPR1 // EXPR2 returns the value of EXPR1 if it's defined, otherwise, the value of EXPR2 is returned. (EXPR1 is evaluated in scalar context, EXPR2 in the context of // itself). Usually, this is the same result as defined(EXPR1) ? EXPR1 : EXPR2 (except that the ternary-operator form can be used as a lvalue, while EXPR1 // EXPR2 cannot, and EXPR1 will only be evaluated once). This is very useful for providing default values for variables. If you actually want to test if at least one of $a and $b is defined, use defined($a // $b).

Upvotes: 46

mpapec
mpapec

Reputation: 50637

Check for Logical Defined-Or in perlop, it is similar to || but it checks for undef value (not false one).

Although it has no direct equivalent in C, Perl's // operator is related to its C-style or. In fact, it's exactly the same as ||, except that it tests the left hand side's definedness instead of its truth.

So in short,

my $abc = delete $args{ 'abc' } // croak 'some information!';

will croak when $args{ 'abc' } returns undef value.

Upvotes: 12

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