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ValueTypeCache - A role to cache Value Type classes


use ValueTypeCache;

sub id(%h --> Str:D) {
    %h<x> //= 0;
    %h<y> //= 0;

class Point does ValueTypeCache[&id] {
    has $.x;
    has $.y;

say Point.new.WHICH;  # Point|0,0

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


The ValueTypeCache role mixes the logic of creating a proper ValueType class and making sure that each unique ValueType only exists once in memory, into a class.

The role takes a Callable parameterization to indicate how a unique ID should be created from the parameters given (as a hash) with the call to the new method. You can also adapt the given hash making sure any default values are properly applied. If there's already an object created with the returned ID, then no new object will be created but the one from the cache will be returned.

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.


Elizabeth Mattijsen liz@raku.rocks

Source can be located at: https://github.com/lizmat/ValueTypeCache . Comments and Pull Requests are welcome.

If you like this module, or what I’m doing more generally, committing to a small sponsorship would mean a great deal to me!


Copyright 2020, 2021, 2024 Elizabeth Mattijsen

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