Struct HashMapWitness 

pub struct HashMapWitness<K>(/* private fields */);

Re-exports HashMapWitness, the HKT witness for HashMap<K, V>. HashMapWitness<K> is a zero-sized type that acts as a Higher-Kinded Type (HKT) witness for the HashMap<K, V> type constructor, where the key type K is fixed.

It allows HashMap to be used with generic functional programming traits like Functor and Foldable by fixing one of its type parameters.

Trait Implementations

impl<K> Foldable<HashMapWitness<K>> for HashMapWitness<K>

where K: Hash + Eq + 'static,

fn fold<A, B, Func>(fa: HashMap<K, A>, init: B, f: Func) -> B

where Func: FnMut(B, A) -> B,

Folds (reduces) a HashMap into a single value.

Applies the function f cumulatively to the accumulator and each key-value pair of the hash map, starting with an initial accumulator value.

Arguments

• fa: The HashMap to fold.
• init: The initial accumulator value.
• f: The folding function, which takes the accumulator and a key-value pair.

Returns

The final accumulated value after processing all elements.

impl<K> Functor<HashMapWitness<K>> for HashMapWitness<K>

where K: Hash + Eq + Clone + 'static,

fn fmap<A, B, Func>( m_a: <HashMapWitness<K> as HKT2<K>>::Type<A>, f: Func, ) -> <HashMapWitness<K> as HKT2<K>>::Type<B>

where Func: FnMut(A) -> B,

Implements the fmap operation for HashMap<K, V>.

Applies the function f to each value in the hash map, producing a new hash map with the same keys but transformed values.

Arguments

• m_a: The HashMap to map over.
• f: The function to apply to each value.

Returns

A new HashMap with the function applied to each of its values.

impl<K> HKT for HashMapWitness<K>

type Type<V> = HashMap<K, V>

Specifies that HashMapWitness<K> also acts as a single-parameter HKT, where the K parameter is considered part of the “witness” itself.

impl<K> HKT2<K> for HashMapWitness<K>

type Type<V> = HashMap<K, V>

Specifies that HashMapWitness<K> represents the HashMap<K, V> type constructor with a fixed key type K.