note
eyepopslikeamosquito
<P>
Your original code with strict and warnings:
<CODE>
use strict;
use warnings;
sub twice { 2 * $_[0] }
my @a = map twice, 1..3;
print "@a\n";
</CODE>
gives the warning
<I>"Use of uninitialized value $_[0] in multiplication (*) at map1.pl line 3".</I>
</P>
<P>
This is how it should be written:
<CODE>
use strict;
use warnings;
sub twice { 2 * $_[0] }
my @a = map twice($_), 1..3;
print "@a\n";
</CODE>
which produces <CODE>2 4 6</CODE> as expected.
</P>
<P>
BTW, Conway, in
<a href="http://shop.oreilly.com/product/9780596001735.do">Perl Best Practices</a>, chapter 8,
recommends always using the block
form of [doc://map], not the expression form that you are using.
The expression form might be faster than the block form
though
(if that matters, you should benchmark it).
</P>
1008163
1008166