Tie::Coupler - Tie based implementation of coupled scalars


 use Tie::Coupler;

 my $options = { fconvert => \&double,
                 rconvert => \&half,
                 init     => 1,

 my $impl = new Tie::Coupler($var, $coupled, $options);

 $var = 2;
 print "$var, $coupled\n";   ## Would print: 2, 4

 $coupled = 6;
 print "$var, $coupled\n";   ## Would print: 3, 6

 $var = 5;
 print "$var, $coupled\n";   ## Would print: 5, 15

 $impl->decouple();          ## The two scalars are now independent
                             ## of each other now

 sub double { my ($val) = @_; $val * 2; }
 sub triple { my ($val) = @_; $val * 3; }
 sub half   { my ($val) = @_; int($val / 2); }


Tie::Coupler provides a mechanism by which you can couple two scalars. That is the value of the coupled scalar would determined by the value of the scalar to which it is coupled. The code referenced by the options fconvert and rconvert determine the relation between the two scalars.

The complexity/functionality of the coupling is only limited by your sense of imagination. The simplest form of coupling is a one to one coupling wherein the conversion functions are undefined. In this form of coupling the two scalars would have the same value at any point of time.



Creates a new coupling. It takes two mandatory parameters, the first one VAR is the scalar to be coupled and second parameter COUPLED is the scalar to which VAR is coupled. OPTIONS is an optional parameter specifying the behaviour of the coupling. The options are passed to the constructor as a hash reference. The following are the valid keys and their corresponding effect on the coupling:

   Option      Type              Default
   -------     ----              -------
   fconvert    Code Reference     None
   rconvert    Code Reference     None
   init        Boolean             0

The constructor returns the implementation object that gives the coupled scalar the desired functionality. This implementation object can be used to alter the behaviour of the coupling by calling the appropriate methods.

After the constructor successfully creats the coupling, the two scalars can be used as normal scalar variables. But the magical spell (coupling) cast on the scalars would mean that at any point the value held by the scalars would be based on:

     1. The value of the other scalar 
     2. The characteristics of coupling as specified by the
        conversion routines (fconvert & rconvert)


fconvert => CODEREF

This options defined the callback to be invoked whenever the COUPLED scalar's value changes. The value of the COUPLED scalar is passed as an implicit parameter to this function. The code reference can be specified in one of the following ways:

1. As a code reference - \&function 2. As an anonymous function - sub { function(); } 3. As an array reference - [ $obj, $method, @params ]

The value returned by the function referred by fconvert would be used to determine the relation between the two scalars in the forward direction.

rconvert => CODEREF

Same as fconvert, but determines the relation between the two scalars in the reverse direction.

init => BOOLEAN

If this option is TRUE, then the value of the coupled scalars would be initialized based on the conversion functions.


$impl->fconvert (CODEREF)

Utility method to set the value of the fconvert function.

$impl->rconvert (CODEREF)

Utility method to set the value of the fconvert function.

$impl->decouple ()

Decouples the scalars, releasing the scalars from the magical spell. Once decoupled the scalars continue to behave like normal perl scalars.


The code has not been fully optimized in terms of processing speed and memory utilization. Every read/write access on a coupled scalar has a constant overhead. The magnitude of the overhead is determined purely by the complexity of the conversion routine(s).


May be lot of them :-), but hopefully none. Bug reports, fixes, suggestions or feature requests are most welcome.


Copyright (c) 2001-02 Arun Kumar U <> All rights reserved.

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


Arun Kumar U <>, <>


perl(1), perltie(1)

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