in reply to Getting the next array element while still keeping the current one

Interesting problem. Here is something... 

#!/usr/local/bin/perl

use warnings;
use strict;

init( [ qw/2 3 5 polka dot bikini/ ] );

my $index = 3;  #  'polka'
my ($current , $next , $prev ) =  get($index);

printf "%s\n%s\n%s\n"
  , $current , $next , $prev;


{ my ($old , $cursor , $size , @array);

  sub init
  { my $a_ref = shift;
    @array = @{$a_ref};
    $size = scalar @array or die "empty array\n";
    $cursor = 0;
  }

  sub get
  { $cursor = shift;
    $old = $cursor++;
    return ( current() , next_() , prev() );
  }

  sub current
  { return $array[$old];
  }

  sub prev
  { return ($old -1) >= 0 ?  $array[ $old -1 ] : undef;
  }

  sub next_
  { return ($old +1) < $size ? $array[ $old +1 ] : undef;
  }
}

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From the looks of it, it seems something like it would already have been in existence on CPAN. Anyway ...

Mind that one can easily ignore some/all of the return values; above is just one way of the using the-code-that-wants-to-be-a-module. Needless to say that current(), next_(), and prev() can be called directly as desired.

UPDATE: Return of references to prev() and next_() is changed to the return of values they would have actually returned.

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Re: Re: Getting the next array element while still keeping the current one
by parv (Parson) on May 02, 2004 at 02:45 UTC

    Well here is another update. I did not like expanding the array on initializtion; code below has some other clarifications and enough changes to warrant another reply.

    #!/usr/local/bin/perl

use warnings;
use strict;

my @in = qw/2 3 5 polka dot bikini/;

#  Help the helper code help us
init( \@in );

foreach (0 .. scalar @in -1)
{
  printf " Current: %s\n    Next: %s\nPrevious: %s\n"
    , map { defined $_ ? $_ : 'undefined' }
        #
        #  Let something else fetch the values (in forward direction o
+nly)
        get( $_ )
        #
        #  Do it yourself
        #sub { move_fore(); ( current() , next_() , prev() ); }->()
    ;


  print "\n";
}

#  Helper code
{ my ($old , $cursor , $size , $array);

  sub init
  { $array = shift;
    $size = scalar @{$array} or die "empty array\n";
    $old = $cursor = 0;
  }

  sub get
  { $cursor = shift;
    die "no index given\n" unless defined $cursor;
    move_fore();
    return ( current() , next_() , prev() );
  }

  sub current
  { return $array->[$old];
  }
  sub prev
  { return ($old -1) >= 0 ?  $array->[ $old -1 ] : undef;
  }
  sub next_
  { return ($old +1) < $size ? $array->[ $old +1 ] : undef;
  }

  sub move_fore { $old = $cursor++; }
  sub move_back { $old = --$cursor; }
}

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