[oak perl] Can't modify map iterator in scalar assignment?

[Belden Lyman]

Hi Eric,

On Wed, 2004-12-08 at 17:43, Eric Chen wrote:
> Hi,
> I have the following code
> 
> my $p=qw(1 3 4);

This does not create an array reference; it assigns a list
to a scalar. Instead this should read

  my $p = [ 1, 3, 4 ] ;

or if you like using qw()

  my $p = [ qw( 1 3 4 ) ];

"perldoc perlref" for more info on creating and accessing
references.

> my @array;

> if($p){

Since $p is (supposed to be :) an array reference, it would
be better to use

  if ( defined $p->[0] ) {

>   map{$array[$_]='selected'} @{$p};
> }
> else{
>   $array[0]='selected';
> }
> which works fine when I try to use triary operator
> 

Are you sure it's working fine? When I look at @array after
it's been assigned using that map, I see this:

     #!/usr/bin/perl
     use Data::Dumper;

     my $p = qw(1 3 4);
     my @array;
     map{$array[$_]='selected'} @{$p};
     print Dumper \@array;
     __END__
     $VAR1 = [];

...nothing's set.

>  ($p)? map{$array[$_]='selected'} @{$p} :
> $array[0]='selected';
> 

You don't need map here, you can assign via an array slice.
"perldoc perldata" and search for "A slice accesses several
elements of a list".

Here's your code, tweaked a bit:

  my $p = [ 1, 3, 4 ];
  my @array;

  if ( defined $p->[0] ) {
    # here's the array slice
    @array[ @{$p} ] = ( 'selected' ) x scalar @{$p};
  }
  else {
    $array[0] = 'selected';
  }

Belden