I'm trying to understand the map function in perl and have been studying David's response to my earlier query.
When David calls his iterate function, why does he not need to use the keyword "sub"?
Because he used prototypes instead.
Also, can someone elaborate on his use of prototyping here when he defines function iterate? I don't understand the "&@".
They make the function expect a coderef followed by a list.
And, what about the use of the keyword "for". Should that not be "foreach"?
Those are synonymous (at least as keywords...).
Lastly, I tried to rewrite the code so I could understand it. Why does not this work?
sub iterate{ my $code = shift;
print " begin function iterate\n"; foreach $x (@_) { &$code($x) ; }
print " end function iterate\n"; }
iterate ({ print "Hello $_\n" }, @data);
This is one way to make it "work":
sub iterate {
my $code = shift;
print " begin function iterate\n";
foreach my $x (@_) { &$code($x) ; }
print " end function iterate\n";
}
iterate ( sub { print "Hello $_[0]\n" }, @data);
--------------^^^----------------^^^^^'sub' makes the block a coderef, and since you are setting $x in your foreach loop, $_ is not set.
An alternative:
sub iterate(&@) {
my $code = shift;
print " begin function iterate\n";
foreach my $x (@_) { &$code($x) ; }
print " end function iterate\n";
}
iterate { print "Hello $_[0]\n" } @data;-- Gunnar Hjalmarsson Email: http://www.gunnar.cc/cgi-bin/contact.pl
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