Pairs

A single key-to-value association — the building block of hashes and named args.

A Pair links one key to one value, written key => value. Pairs are the elements of a hash, the form of named arguments, and a value in their own right.

The fat-arrow form #

my $p = a => 1;
say $p;
say $p.key;
say $p.value;

a => 1
a
1

Colon-pair forms #

:key(value) is the same Pair; :key alone means key => True, and :key<word> uses a quoted-word value. These are exactly the forms used for named arguments.

say (:x(5));
say (:done);
my $q = :name<Ada>;
say $q;

x => 5
done => True
name => Ada

Notes #

• :$var is shorthand for var => $var — the pattern behind named arguments.
• A list of Pairs is what initialises a hash: my %h = a => 1, b => 2.
• :!key is key => False, the negated colon-pair — common for turning a flag off.