Course of Raku / Essentials / Associative data types

Pairs

A pair is a data structure that keeps a name and a value. They form a solid object which can be stored in a scalar variable. Here is an example of how you create a pair:

my $pair = name => 'Anna';

The type of the variable $pair is Pair:

say $pair.WHAT; # (Pair)

It is possible to access the name and the value separately by using the corresponding methods key and value:

say $pair.key; # name
say $pair.value; # Anna

An important feature of pairs is they are immutable objects. It means that you cannot assign a new value or give a new name to an existing pair. But you can assign a completely new pair to the same variable, of course:

my $pair = name => 'Anna';
$pair = name => 'John';
say $pair.value; # John

Subscripting

There is another method of reading the value of a pair. You can subscript it with the name of its key between angle brackets. This is how you do that:

say $pair<name>;

Notice that there is no need to quote the name of the key if it contains no spaces. If it does, things become a bit stricter:

my $pair = 'employee name' => 'Julie Madelon';
say $pair{'employee name'};

Do not miss the fact that curly braces are used this time.

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