push, pop, shift and unshift were all present in Perl 1, released in 1987. It's surprising how many features it had.

Be careful not to confuse lists and arrays, though, as you can't use any of these operators to modify a list.

You may be interested in learning splice, map, and grep as well. Perl is truly rich in methods of manipulating lists and arrays.

Pronouncements like your programming friend made about what can be done with lists usually have a hidden assumption about how the list is implemented at low level. That could be linked nodes, fixed records adjacent in memory, or some flavor of tree. Each has strengths and weaknesses in the fundamental operations of insertion, deletion, searching, and indexing.

After Compline,
Zaxo

I'm not sure that shift and unshift are so amazingly unique. After all, it's possible to simulate their behaviour with push and pop

Hmm, after tinkering quickly with some code, this is all I could come up with.

#!/usr/bin/perl -w

my @data = qw/1 2 3 4 5/;
print "Data is " . join ( ":", @data ) . "\n";

@data = reverse @data;
my $foo = pop @data;
@data = reverse @data;
print "Data is " . join ( ":", @data ) . "\n";

@data = reverse @data;
push ( @data, 17 );
@data = reverse @data;
print "Data is " . join ( ":", @data ) . "\n";
[download]

So maybe shift and unshift are useful after all. Is there an easier way to simulate the behaviour that I've missed?

It's not only a matter of merely simulating the behavior of shift and unshift, it may have a lot to do with execution efficiency since a reverse is an expensive operation. It involves creating a new list and populating it with the elements of the original in O(n) time (n = length of the list).

A shift is typically O(1) time since it involves just taking out the first element of which you have the address anyway -- it's the start of the list -- and making the second element the first. The same holds for unshift which is a simple insertion at the beginning of the list.

So for reasons of efficiency, you really want shift and unshift, not only to make code look more elegant.

Hope this helps, -gjb-

And for anyone concerned with the speed implications of shift and unshift (and push and pop for that matter) they must check out lhoward's marvellous Shift, Pop, Unshift and Push with Impunity!.
HTH

_________
broquaint