count method

int count([
  1. bool test(
    1. T element
    )?
])

Returns the number of elements that matches the test.

If not test is specified it will count every element.

Example:

[1, 2, 3, 13, 14, 15].count();             // 6
[1, 2, 3, 13, 14, 15].count((n) => n > 9); // 3

Implementation

int count([bool Function(T element)? test]) {
  test ??= (_) => true;
  if (isEmpty) return 0;
  return map((element) => test!(element) ? 1 : 0)
      .reduce((value, element) => value + element);
}