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This is available as Dict\filter_async in the www repository.

Returns a new dict containing only the values for which the given async predicate returns true

namespace HH\Lib\Dict;

function filter_async<Tk as arraykey, Tv>(
  KeyedContainer<Tk, Tv> $traversable,
  (function(Tv): Awaitable<bool>) $value_predicate,
): Awaitable<dict<Tk, Tv>>;

For non-async predicates, see Dict\filter().

Time complexity: O(n * p), where p is the complexity of the synchronous portions of $value_predicate Space complexity: O(n)

The IO operations for each of the calls to $value_predicate will happen in parallel.