Course of Raku / Advanced / Containers / Subscript adverbs 🆕

Keys, values, and pairs

Other adverbs change what a subscript gives back. By default, a subscript returns the value; these return more:

• :v — the value (the default)
• :k — the key (or index)
• :kv — both the key and the value
• :p — a Pair of key and value

For an array, the “key” is the index:

my @a = 10, 20, 30;

say @a[1]:kv; # (1 20)
say @a[1]:p;  # 1 => 20

@a[1]:kv returns the index and the value together as a list, and @a[1]:p returns them as a pair.

The same works for hashes, and it is especially handy across a slice of several keys at once:

my %h = a => 1, b => 2, c => 3;

say %h<a c>:kv; # (a 1 c 3)

Here, a two-key slice comes back as alternating keys and values. These adverbs are what map, for, and friends often rely on when you want to process keys and values side by side, without splitting the work into separate lookups.

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