interface Mapper<A, B> {
B map(A a);
}
<A, B> Iterable<B> mapperConvert(Iterable<A> x, Mapper<A, B> m) {
Collection<B> y = new LinkedList<B>();
for(A a : x)
y.add(m.map(a));
return y;
}
Problem resolved? LinkedList?
What if we want to map something that is not only not Iterable, but it makes no sense for it
to be Iterable? i.e. we couldn't even implement the interface if we wanted to.
Should we concede and use dynamic typing — any object that supports the map method? Or
perhaps concede Java's static type system and use reflection?
Perhaps we want to do a bit more, such as remove elements of a certain criteria as we map?