delete on tied variables

[cmac]

I'm writing a module that implements tied interfaces. The description of the tied interface describes the DELETE function for both arrays and hashes as applying to only one entry/element.

The description of the delete function says that it can be used on a "hash element, array element, hash slice, or array slice".

Q1: What is a hash slice and how is one written in Perl?

Q2: if a delete function in a Perl program specifies a slice, will the interpreter break it up into individual calls to DELETE?

Q3: if not, what are the operands to DELETE that express a slice, for both an array and a hash?

If there are other pages that cover this subject, please tell me.

Thanks be to Perl Monks,
cmac
www.animalhead.com

[ikegami]

What is a hash slice and how is one written in Perl?

A means of selecting multiple elements for fetching or setting. An example would be @hash{ 'key1', 'key2', ... }. See perldata for details.

if a delete function in a Perl program specifies a slice, will the interpreter break it up into individual calls to DELETE?

Yes.

{
   package Tester;
   use Tie::Hash qw();
   our @ISA = 'Tie::StdHash';
   sub DELETE {
      my $self = shift;
      print("DELETE @_\n");
      $self->SUPER::DELETE(@_)
   }
}

{
   tie my %hash, 'Tester';
   %hash = (
      a => 1,
      b => 2,
      c => 3,
      d => 4,
   );
   delete @hash{qw( b c )};
   print(join(' ', keys %hash), "\n");
}

DELETE b
DELETE c
a d

If there are other pages that cover this subject, please tell me.

• tie
• Tie::Scalar
• Tie::Array
• Tie::Hash
• Tie::Handle

Update: Formatting changes. Switched from using array to using hash in DELETE test.

[dragonchild]

Perl is opensource. As such, there are dozens of modules on CPAN that use tying. One example is DBM::Deep. It implements tying for both arrays and hashes and it implements (nearly) every single method that the tie interface provides for arrays and hashes. If DBM::Deep doesn't do it or worry about it, then it's probably not something you need to worry about. (If I'm mistaken, I need to know cause it's a bug in DBM::Deep!)