NAME

Tie::Reduce - a scalar that reduces its old and new values to a single value

SYNOPSIS

  use Tie::Reduce;
  
  tie my $sum, "Tie::Reduce", sub { $a + $b }, 0;
  
  $sum = 1;
  $sum = 2;
  $sum = 3;
  $sum = 4;
  
  say $sum;  # 10

This is similar in spirit to:

  use List::Util qw(reduce);
  
  my $sum = reduce { $a + $b } 0, 1, 2, 3, 4;
  
  say $sum;  # 10

DESCRIPTION

Tie::Reduce allows you to create a scalar which when assigned a new value, passes its old value and assigned value to a coderef, and uses the result as its new value.

Tie API

tie($scalar, "Tie::Reduce", \&reduction, $initial_value)

Ties the scalar using the given coderef for reducing values.

The initial value is optional and will default to undef. This value is set to the scalar immediately without being passed through the reduction coderef.

$scalar (FETCH)

Returns the current value of the scalar.

$scalar (STORE)

Sets the current value to the result of passing the old value and the stored value into the coderef.

Within the coderef, the old and new values are available as the special package variables $a and $b (like reduce from List::Util and the Perl built-in sort function).

Object API

The object API is not generally useful for end users of Tie::Reduce, with the possible exception of set_value. It is mostly documented for people wishing to subclass this module.

Tie::Reduce->new($coderef, $initial_value)

Constructor.

This is called by TIESCALAR.

tied($scalar)->get_value

Returns the current value of the scalar variable.

This is called by FETCH.

tied($scalar)->set_value($value)

Sets the scalar variable without passing it through the coderef.

tied($scalar)->assign_value($value)

Sets the scalar variable, passing it through the coderef.

Subclassers should be aware that this method uses caller to find the name of the calling package and access package variables $a and $b.

This is called by STORE.

tied($scalar)->get_coderef

Returns the coderef being used to reduce values.

tied($scalar)->_set_coderef($coderef)

Sets the coderef used to reduce values. This is only documented for people subclassing Tie::Reduce. Variables tied with Tie::Reduce are confusing enough without changing the coderef part-way through the variable's lifetime!

BUGS

Please report any bugs to http://rt.cpan.org/Dist/Display.html?Queue=Tie-Reduce.

SEE ALSO

"tie" in perlfunc, perltie, Tie::Scalar.

AUTHOR

Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE

This software is copyright (c) 2018 by Toby Inkster.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

DISCLAIMER OF WARRANTIES

THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.