joshweir joshweir - 5 months ago 14
Perl Question

What does "last" do in Perl?

In the code below, what does

last
do in the while loop? I get that if the
$matrix[$i][$j]{pointer}
variable equals
"none"
it calls
last
but what does it do?

Also why does the $matrix variable include score and pointer using curly braces?
{score}
, I read this as the 3rd dimension in an array, but is this something else? Couldn't find anything on google about this. Thanks!

my @matrix;
$matrix[0][0]{score} = 0;
$matrix[0][0]{pointer} = "none";
#populate $matrix with more stuff

while (1) {
last if $matrix[$i][$j]{pointer} eq "none"; #<-what is this "last" doing?
#do some more stuff here
}

Answer

Available uses for last command:

  • last LABEL

  • last EXPR

  • last

According to Perl's documentation:

The last command is like the break statement in C (as used in loops); it immediately exits the loop in question. If the LABEL is omitted, the command refers to the innermost enclosing loop. The last EXPR form, available starting in Perl 5.18.0, allows a label name to be computed at run time, and is otherwise identical to last LABEL . The continue block, if any, is not executed:

 LINE: while (<STDIN>) {
        last LINE if /^$/;  # exit when done with header
        #...
    }

last cannot be used to exit a block that returns a value such as eval {} , sub {} , or do {} , and should not be used to exit a grep or map operation. Note that a block by itself is semantically identical to a loop that executes once. Thus last can be used to effect an early exit out of such a block.