typed<K, V>  static method 
Creates a wrapper that asserts the types of keys and values in base.
This soundly converts a Map without generic types to a Map<K, V> by
asserting that its keys are instances of E and its values are instances
of V whenever they're accessed. If they're not, it throws a TypeError.
Note that even if an operation throws a TypeError, it may still mutate
the underlying collection.
This forwards all operations to base, so any changes in base will be
reflected in this. If base is already a Map<K, V>, it's returned
unmodified.
Implementation
@Deprecated('Use map.cast<K, V> instead.')
static Map<K, V> typed<K, V>(Map base) => base.cast<K, V>();