NAME

 Tie::Watch() - place watchpoints on Perl variables.

SYNOPSIS

 use Tie::Watch;

 $watch = Tie::Watch->new(
     -variable => \$frog,
     -debug    => 1,
     -fetch    => [\&fetch, 'arg1', 'arg2', ..., 'argn'],
     -store    => \&store,
     -destroy  => sub {print "Final value=$frog.\n"},
 }
 %vinfo = $watch->Info;
 $args  = $watch->Args(-fetch);
 $val   = $watch->Fetch;
 print "val=", $watch->Say($val), ".\n";
 $watch->Store('Hello');
 $watch->Delete;

DESCRIPTION

 . alter a variable's value
 . prevent a variable's value from being changed
 . invoke a Perl/Tk callback when a variable changes
 . trace references to a variable

Callback format is patterned after the Perl/Tk scheme: supply either a code reference, or, supply an array reference, and pass the callback code reference in the first element of the array, followed by callback arguments. (See examples in the Synopsis, above.)

Tie::Watch provides default callbacks for any that you fail to specify. Other than negatively impacting performance, they perform the standard action that you'd expect, so the variable behaves ``normally''.

Here are two callbacks for a scalar. The fetch (read) callback does nothing other than illustrate the fact that it returns the value to assign the variable. The store (write) callback uppercases the variable.

 my $fetch_scalar = sub {
     my($self) = @ARG;
     $self->Fetch;
 };

 my $store_scalar = sub {
     my($self, $new_val) = @ARG;
     $self->Store(uc $new_val);
 };

Here are fetch and store callbacks for either an array or hash. They do essentially the same thing as the scalar callbacks, but provide a little more information.

 my $fetch = sub {
     my($self, $key) = @ARG;
     my $val = $self->Fetch($key);
     print "In fetch callback, key=$key, val=", $self->Say($val);
     my $args = $self->Args(-fetch);
     print ", args=('", join("', '",  @{$args}), "')" if $args;
     print ".\n";
     $val;
 };

 my $store = sub {
     my($self, $key, $new_val) = @ARG;
     my $val = $self->Fetch($key);
     $new_val = uc $new_val;
     $self->Store($key, $new_val);
     print "In store callback, key=$key, val=", $self->Say($val),
       ", new_val=", $self->Say($new_val);
     my $args = $self->Args(-store);
     print ", args=('", join("', '",  @{$args}), "')" if $args;
     print ".\n";
     $new_val;
 };

In all cases, the first parameter is a reference to the Watch object. You can use this to invoke useful class methods.

METHODS

$watch = Tie::Watch->new(-options => values);

-debug = 1 to activate debug print statements internal to Tie::Watch.

Specify any of the following relevant callback parameters, in the format described above: -fetch -store -destroy -clear -delete -exists -firstkey and/or -nextkey.

$args = $watch->Args(-fetch);

$watch->Delete;

$watch->Fetch; $watch->Fetch($key);

%vinfo = $watch->Info;

 %vinfo = {
     -variable =>  SCALAR(0x200737f8)
     -fetch    =>  ARRAY(0x200f8558)
     -store    =>  ARRAY(0x200f85a0)
     -destroy  =>  ARRAY(0x200f86cc)
     -debug    =>  '1'
     -value    =>  'HELLO SCALAR'
     -legible  =>  above data formatted as a list of string, for printing
 }

For array and hash Watch objects, the 'value' key is replaced with a 'ptr' key which is a reference to the parallel array or hash. Additionally, for hashes, there are key/value pairs to the hash-specific callback options.

$watch->Say($val);

$watch->Store($new_val); $watch->Store($key, $new_val);

EFFICIENCY CONSIDERATIONS

AUTHOR

HISTORY

 lusol@Lehigh.EDU, LUCC, 96/05/30
 . Original version 0.92 release, based on the Trace module from Hans Mulder,
   and ideas from Tim Bunce.

 lusol@Lehigh.EDU, LUCC, 96/12/25
 . Version 0.96, release two inner references detected by Perl 5.004.

 lusol@Lehigh.EDU, LUCC, 97/01/11
 . Version 0.97, fix Makefile.PL and MANIFEST (thanks Andreas Koenig).
   Make sure test.pl doesn't fail if Tk isn't installed.

COPYRIGHT

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.