Arguments are passed "by reference" in perl subs, allowing in-place modification. So, you can do things like the following: 
sub double_it { $_[0] *= 2 }
my $x = 1;
print "\$x is $x\n";
double_it($x);
print "\$x is now $x\n";

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and have 
$x is 1
$x is now 2

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When you use: 
my ($url, @list) = @_;

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you're creating copies of the input arguments, so when you modify them you don't have any side-effect outside the function. In your code, these copies are inefficient and not needed, because the code is quite simple and you don't perform in-place modifications. So, you simply grab the first parameter, and use the resulting @_ instead of @list, saving space and time: 
sub links {
   my $url = shift;      # This removes the first element of @_
   map { "$url/$_" } @_; # You don't need return :)
}

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I also find this construct useful when porting functions into classes. When you transform a plain function in a class/object method, the first parameter that's passed is the class name/reference to object, so if you have a function: 
sub some_func {
   # ... some stuff?
   my ($foo, $bar, $baz) = @_;
   # ... other stuff
}

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you can transform it at once: 
sub some_func {
   my $self = shift;
   # Maybe do some checks with $self first?
   # ... some stuff?
   my ($foo, $bar, $baz) = @_;
   # ... other stuff
}

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in a much cut-and-paste fashion. But do check the code!

Flavio (perl -e "print(scalar(reverse('ti.xittelop@oivalf')))")

Don't fool yourself.

In reply to Re^3: Turning foreach into map? by polettix
in thread Turning foreach into map? by ghenry

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