sum method

num sum(num addend(E))

Returns the sum of all the values in this iterable, as defined by addend.

Returns 0 if this is empty.

Example:

['a', 'aa', 'aaa'].sum((s) => s.length); // 6.

Implementation

num sum(num Function(E) addend) {
  if (isEmpty) {
    return 0;
  }
  return fold(0, (prev, element) => prev + addend(element));
}