sum<TNum extends num> method

TNum sum<TNum extends num>([ TNum selector(T)? ])

Calculates the sum of the elements in an iterable, optionally using selector to obtain the value to be summed.

Iterates over the entire iterable, passing each element to the selector function and adding its return value to a running total. Once iteration is complete, the total is returned.

The type of the returned total is dependent on the value returned by the selector function. If all values are int, the return value of sum will be int. If all values are double, the return value of sum will be double. If all values are num or there is a combination of int and double, the return value of sum will be num.

When the type of the iterable is a numeric primitive (e.g. int, double, or num), the selector function can be omitted. If so, the elements themselves are added to the running total.

If the type of the iterable is not a numeric primitive, the selector function must be provided. Otherwise, a StateError is thrown.

If the iterable is empty, 0 is returned.

Example:

void main() {
  final listA = [1, 2, 3, 4];
  final result = list.sum();

  // Result: 10
}

Implementation

TNum sum<TNum extends num>([TNum Function(T)? selector]) {
  var selectorImpl = selector;
  var total = TNum == int ? 0 : 0.0;

  if (selectorImpl == null) {
    if (T == num || T == int || T == double) {
      selectorImpl = (n) => n as TNum;
      total = T == int ? 0 : 0.0;
    } else {
      throw ArgumentError(
          "If T isn't a subtype of num, selector must not be null.");
    }
  }

  for (final n in this) {
    total += selectorImpl(n);
  }

  return total as TNum;
}