Re: Best Hash Practices?

> All ideas are welcome...

ok ... what about this?

use strict;
use warnings;
 
 
sub xdefined  {
  my $ref=shift;
  my $type;
  while ( my $key=shift) {
    $type= ref($ref);
    if    ( $type eq "HASH"  ) {
      return unless defined $ref->{$key};
      $ref=$ref->{$key}
    }
    elsif ( $type eq "ARRAY" ) {
      return unless  defined $ref->[$key];
      $ref=$ref->[$key]
    }
    else                       # no reference
      { return }; 
  }
  return defined $ref;
}
 
 
my $h->{a}->[2]->{c}=0;
$\="\n";
$,=":";
print 5, xdefined($h,"a",2,"c",4,"e");
print 4, xdefined($h,"a",2,"c",4);
print 3, xdefined($h,"a",2,"c");
print 2, xdefined($h,"a",2);
print 1, xdefined($h,"a");
print 0, xdefined($h);
[download]

-->

5
4
3:1
2:1
1:1
0:1
[download]

Using prototypes like (\[%@]@) can further "beautify" the interface! 8)

Cheers Rolf

Comment on Re: Best Hash Practices? Select or Download Code

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Re^2: Best Hash Practices? by DamianKaelGreen (Acolyte) on Oct 12, 2009 at 17:51 UTC
Yes, this is the direction I was headed with this too... It would be nicer though if the input to the function was just the autovivified list of keys though, so we could maintain a more usual appearance, like: `print 6, isDefined($h{"a"}{2}{c}{4});` This is a kind of standard function that I think should be developed more thoroughly for everyone to use regularly; Either that, or the fundamentals of the way a multidimensional hash is handled should possibly be re-evaluated to recognize when something is being created vs when it's being tested...	[reply] [d/l]
Re^3: Best Hash Practices? (tie) by LanX (Saint) on Oct 12, 2009 at 20:14 UTC
Hi I know what you mean but the syntax you're proposing is not feasible, since it's the arrow operator which is autovivifying! `isDefined($h{"a"}->{2}->{c}->{4});` [download] So when isDefined comes into action it's already to late! Anyway one can easily extend the syntax of my approach to make it "smoother"! `xdefined(%h => qw/a 2 c 4/)` [download] or `xdefined(%h => "a",2,"c",4)` [download] But IMHO (within the boundaries of perl) the syntactically "prettiest" way to go would be to use a tied copy of your hash, like this you may be able to write `novivi(%h)->{a}{2}{c}{4}` [download] `%h2=novivi(%h)` should be an empty hash with a hash-tie which mirrors safely the structure of %h. Such that `$h2{a}` is only be defined iff `$h{a}` is defined and all the automatically vivified structures in `$h2{a}{2}{c}{4}` are automatically tied hashes bound to the corresponding structures in %h. Well ... I think this is feasible, BUT should come with a significant performance penalty compared to my first approach, since ties are expensive. Cheers Rolf	[reply] [d/l] [select]