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List::Agnostic - be a list without knowing how


use List::Agnostic;

my $list = (1, 2, 4, 8, 16, 32, 64, 128);

class MyList does List::Agnostic {
    method AT-POS(\pos) { $list[pos]  }
    method elems()      { $list.elems }

my @m is MyList;                  # static at runtime
say @m[3];  # 8

class MyOtherList does List::Agnostic {
    has $!list is built;
    method new($list) { self.bless(:$list) }
    method AT-POS(\pos) { $!list[pos]  }
    method elems()      { $!list.elems }

my @o := MyOtherList.new($list);  # settable at runtime
say @o[4];  # 16


This module makes a List::Agnostic role available for those classes that wish to implement the Positional role as an immutable List. It provides all of the List functionality while only needing to implement 4 methods:

Note that contrary to other Agnostic modules, this module assumes that there is an existing data structure to which a Positional interface is needed.

Required Methods

method AT-POS

method AT-POS($position) { ... }  # simple case

Return the value at the given position in the list.

method elems

method elems(--> Int:D) { ... }

Return the number of elements in the list (defined as the index of the highest element + 1).

Optional Methods (provided by role)

You may implement these methods out of performance reasons yourself, but you don't have to as an implementation is provided by this role. They follow the same semantics as the methods on the List object.

In alphabetical order: append, Array, end, gist, iterator, keys, kv, list, List, new, pairs, perl, shape, Slip, Str, values


Elizabeth Mattijsen liz@raku.rocks

Source can be located at: https://github.com/lizmat/List-Agnostic . 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 2024 Elizabeth Mattijsen

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