It becomes clear as what's going on, once we add some print outs at certain critical point (also see comments):
use Data::Dumper;
use strict;
sub prefix_later {
my ($just_once,$and_later) = @_; #passed by calling part, see below
my $ct=0;
return sub {
my (@args) = shift(); #this is just a trick ;-)
print Dumper(\@args);
print "ct = $ct\n"; #will not be reset to zero, becasue of closu
+re
((!$ct++) ? #only true for the first time
sub {
print "sub1\n";
$just_once->(@args); #hi mom
} :
sub {
print "sub2\n";
$and_later->(@args); #this was unneccessary:
$just_once->(@args); #hi mom
}
)->();
}
}
my $hi_mom = prefix_later(
sub { print "hi mom\n"; },#this is just once
sub { print "this was unneccessary:\n"; } #this is and later
);
$hi_mom->() for (1..3);
Outputs:
#first round
$VAR1 = [
undef
];
ct = 0
sub1
hi mom
#second round
$VAR1 = [
undef
];
ct = 1
sub2
this was unneccessary:
hi mom
#third round
$VAR1 = [
undef
];
ct = 2
sub2
this was unneccessary:
hi mom
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