


Tie::Scalar::DecUasye(r3)Contributed Perl DocumentTaitei:o:nScalar::Decay(3)


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       Tie::Scalar::Decay - Scalar variables that decay

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         use Tie::Scalar::Decay;

         tie my $scalar, 'Tie::Scalar::Decay', (
           VALUE => 32,
           FUNCTION => '$value-=1',
           PERIOD => 1
         );

         while($scalar>0) {
           print "$scalar\n";
           sleep(2);
         }


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       This module allows you to tie a scalar variable whose
       value will change regularly with time.  The default
       behaviour is for numeric values to halve every time period
       (a la radioactive decay) and for non-numeric values to be
       unchanged.

       You can specify a custom decay function if you wish.

       The following named parameters are supported:

       `PERIOD'
           Use `PERIOD' to specify the time interval for changes.
           This can be either a numeric value, in which case it
           is taken to be a number of seconds, or the following
           forms are also accepted:

               30s                    every thirty seconds
               10m                    every ten minutes
               1h                     every hour
               1d                     every day

           Assigning a value to the variable causes the timer to
           be reset to zero, so if at t=0 you set a value of 5
           with a timeout of thirty seconds, then wait twenty
           seconds and set the value again, then it will not
           decay until t=50.  The default is a somewhat arbitrary
           5 seconds.

       `VALUE'
           Using the `VALUE' hash key, you can specify an initial
           value for the variable.  Defaults to undef.

       `FUNCTION'
           This is how you can define your own custom decay
           functions.  This can either be a string (in which case



2001-04-11                 perl v5.6.0                          1





Tie::Scalar::DecUasye(r3)Contributed Perl DocumentTaitei:o:nScalar::Decay(3)


           it is evalled as necessary, and should alter the
           variable $value as it sees fit) or it can be a
           coderef, in which case the subroutine is called as
           necessary, with the current value as a parameter.  The
           sub is expected to return the new value.  If you don't
           specify a function, it defaults to one which halves
           the value if it is numeric, or leaves it as it is
           otherwise.

           Note that whilst it may appear that your FUNCTION gets
           called every PERIOD, it isn't really.  In reality, the
           value stored in the tied scalar remains constant, and
           every time you try to read its value, a temporary
           variable is created and FUNCTION gets called the
           appropriate number of times before that is returned,
           thus generating the right illusion.  Therefore, your
           FUNCTION should not depend on such things as the
           absolute time.

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       Plenty, no doubt.  Please tell me if you find any.

       One caveat is that it relies on Time::HiRes.  If your
       system doesn't support this, then you can comment it out
       of the module and it'll still mostly work.  You may get
       hurt by sub-second periods (they still work but the
       granularity of the timer is only a second) and very
       occasionally by boundary conditions if the load on your
       machine is high.  Timing things with 1-second accuracy
       blows goats.

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       David Cantrell <david@cantrell.org.uk>

       This module was inspired by Marcel Grunauer's
       Tie::Scalar::Timeout.

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       Copyright 2001 David Cantrell.

       This module is licensed under the same terms as perl
       itself.

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       Tie::Scalar(3pm), _T_i_e_:_:_S_c_a_l_a_r_:_:_T_i_m_e_o_u_t(3)












2001-04-11                 perl v5.6.0                          2


