update abstract method

ComputedMap<K, V> update(
  1. K key,
  2. V update(
    1. V value
    ), {
  3. V ifAbsent()?,
})

Implementation

ComputedMap<K, V> update(
    // Note that the computed variant is trivial
    K key,
    V Function(V value) update,
    {V Function()? ifAbsent});