Creates an Iterable which generates its elements dynamically.
The generated iterable has count elements,
and the element at index n is computed by calling generator(n).
Values are not cached, so each iteration computes the values again.
If generator is omitted, it defaults to an identity function
on integers (int x) => x, so it may only be omitted if the type
parameter allows integer values. That is, if E is one of
int, num, Object or dynamic.
As an Iterable, new Iterable.generate(n, generator)) is equivalent to
const [0, ..., n - 1].map(generator).
Source
factory Iterable.generate(int count, [E generator(int index)]) {
if (count <= 0) return new EmptyIterable<E>();
return new _GeneratorIterable<E>(count, generator);
}