sum method

num sum(
  1. num addend(
    1. 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) => this.isEmpty
    ? 0
    : this.fold(0, (prev, element) => prev + addend(element));