Indexed list access

Work with positions — kv, antipairs, and the :k adverb on grep/first.

Several methods surface a list's indices alongside (or instead of) its values — for iterating with a counter, or finding where something is rather than what.

kv and antipairs #

.kv flattens to alternating index/value; .antipairs returns value => index pairs.

say <a b c>.kv;
say <a b c>.antipairs;

(0 a 1 b 2 c)
(a => 0 b => 1 c => 2)

.kv is what for @a.kv -> $i, $v { … } iterates.

Indices with :k #

The :k adverb makes grep and first return positions instead of values.

say (10, 20, 30).grep(* > 15, :k);
say (10, 20, 30).first(* > 15, :k);

(1 2)
1

grep(:k) gives every matching index; first(:k) gives the first.

Notes #

• The adverb family is :k (keys/indices), :v (values, the default), :kv (both), and :p (pairs) — they work on grep, first, and hash access alike.
• .pairs on a list gives index => value (the opposite order to .antipairs).
• .kv on a hash yields key/value pairs instead of index/value — the same method, keyed by the container type.