Help language development. Donate to The Perl Foundation

ValueType cpan:ELIZABETH last updated on 2021-01-31



ValueType - A role to create Value Type classes


use ValueType;

class Point does ValueType {
    has $.x = 0;
    has $.y = 0;

say;  # Point|Int|0|Int|0

# fill a bag with random Points
my $bag = bag (^1000).map: { x => (-10..10).roll, y => (-10..10).roll
say $bag.elems;  # less than 1000


The ValueType role mixes the logic of creating a proper ValueType into a class. A class is considered to be a value type if the .WHICH method returns an object of the ValueObjAt class: that then indicates that objects that return the same WHICH value, are in fact identical and can be used interchangeably.

This is specifically important when using set operators (such as (elem), or Sets, Bags or Mixes, or any other functionality that is based on the === operator functionality, such as unique and squish.

The format of the value that is being returned by WHICH is only valid during a run of a process. So it should not be stored in any permanent medium.


The first time the WHICH method (mixed in by this role) is called, it will check all of its attribute values for being a value type. If they all are, then it will construct a ValueObjAt object for its WHICH value, save it for future reference, and return it. If any of the attribute values are not a value type, then an exception will be thrown.


Elizabeth Mattijsen [email protected]

Source can be located at: . Comments and Pull Requests are welcome.


Copyright 2020,2021 Elizabeth Mattijsen

This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.