in reply to Re^7: Perl vs C
in thread Perl vs C

Now you're modifying an array, swapping one value (a list) for another (another list). Calling the array @list doesn't change the fact it's an array. The code below doesn't modify '3' either - it just replaces the value of a variable. 
   my $var = 3;
   $var++;
   say $var;  # Prints 4.

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Re^9: Perl vs C
by Marshall (Canon) on Mar 16, 2009 at 15:00 UTC
    I don't understand what you mean. Sure it is possible to modify a list! Just like in C, I can pass a reference to a list to be modified and it will be modified! In the code below, I am modifying the actual list since the sub uses the reference to that list. 
    #!usr/bin/perl -w
use warnings;

sub modify_list
{
   my $listRef = shift;
   @$listRef = grep{!/^b/}@$listRef;
   #note there is no "return" value here
   #the list has been modified!!!!
}

my @list = ("a1", "b23", "c45", "d1", "b43", "b65");
print join (" ",@list),"\n"; 
#prints: a1 b23 c45 d1 b43 b65

modify_list(\@list);
print join (" ",@list),"\n"; 
#prints a1 c45 d1

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[d/l]

      You've only modified array @list again. No lists were modified.

      You're also wrong about there being no return value. It's just being ignored.

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[d/l]
        1. Yes all Perl subs have a return value. Correct.

        2. Again we are into semantics. I modified the data structure that was passed into the sub by reference. So write some code that modifies a "list". What would that be? Some authors say that @xyz is a list and that xyz is an array variable that defines a list. What's wrong with saying that @xyz is a list? Or that xyz in the context of @ is a list? Or that (@xyz >1) is a list in a scalar context?

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      Just like in C, I can pass a reference to a list to be modified and it will be modified!

      Please demonstrate, with working and tested Perl, how to take a reference to a list without using an array. At that point, I will believe that Perl supports mutable first-class lists as data structures (instead of multiple items on the Perl stack or a series of comma-separated expressions in source code).

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