sumBy<T extends num> method Null safety

T sumBy<T extends num>(
  1. T selector(
    1. int index,
    2. E
    )
)

Returns the sum of all values produced by selector function applied to each element in the collection.

For example:

[jon, amy, joe].sumBy((_, student) => student.score) // => total score

Implementation

T sumBy<T extends num>(T Function(int index, E) selector) =>
    mapIndexed(selector).sum();