map2<C, D> method
Change type of this StateAsync based on its value of type A
and the
value of type C
of another StateAsync.
Implementation
@override
StateAsync<S, D> map2<C, D>(
covariant StateAsync<S, C> m1, D Function(A a, C c) f) =>
flatMap((a) => m1.map((c) => f(a, c)));