in reply to Re: Re: package globals and sort()
in thread package globals and sort()

Just do the actual sort in the MyOrder Package as shown. Note as we pass list references we pass 4 bytes in and 4 bytes out of the MyOrder package. 

package MyOrder;

my %order = ( );

sub SortCriteria {  
  if ( exists $order{$a} and exists $order{$b} ) {
    return $order{$a} <=> $order{$b}
  } elsif ( exists $order{$a} ) {
    return 1
  } elsif ( exists $order{$b} ) { 
    return -1 
  } else { 
    return $a cmp $b 
  } 
}

sub SortMyWay { 
    my $list_ref = shift; 
    return [sort SortCriteria @$list_ref]; 
}

package main;

use strict;

my @foo = qw( j a p h , );

my $bar = MyOrder::SortMyWay(\@foo);
my @bar = @$bar;

print "@bar";

[download]

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

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Re: Re: Re: Re: package globals and sort()
by Anonymous Monk on Apr 19, 2002 at 01:48 UTC
    Won't the @$list_ref cause an array copy? Not to mention the sort itself, and then again on the return. Forgive me, I was never all that clear where perl copies vs refs. Since the list is between 10,000 entries and 1,000,000 entries, I don't want to copy it any more then required.
[reply]

      No there is no copy. If you know about C you will know about *pointers*. Anyway even if you don't all that is passed is a pointer to the original array. @$list_ref just uses the array pointed to by $list_ref. No copy is made. This is why it is efficient to pass array refs to and from subs as you never copy an array you don't have to.

      The is a way to implement things the way you wanted originally by passing $a and $b to the other package but this is far less efficient so don't do it! Here it is just to show you it can be done. We can even localise $a and $b :-) 

      package MyOrder;

use strict;
my %order = ();

sub SortMyWay { 
  my ($a,$b) = @_; 
  if ( exists $order{$a} and exists $order{$b} ) {
    return $order{$a} <=> $order{$b}
  } elsif ( exists $order{$a} ) {
    return 1
  } elsif ( exists $order{$b} ) { 
    return -1 
  } else { 
    return $a cmp $b 
  } 
} 

package main;

use strict;
my @foo = qw( j a p h , );
my @bar = sort { MyOrder::SortMyWay($a,$b) } @foo;
print "@bar";

      [download]

      cheers

      tachyon

      s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

[reply]
[d/l]

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