count method

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

Returns the number of elements in the iterable.

Optionally, a condition can be specified. If so, the total count will be the number of elements for which the condition function returned true.

If the condition parameter is omitted, the count method will call the length property of the iterable. This will either be an O(1) operation or an O(n) operation, depending on the runtime type of the iterable. (e.g. If the iterable is a List, calling count will be an O(1) operation.)

Example:

void main() {
  final list = [0, 1, 2, 3];
  final resultA = list.count();
  final resultB = list.count((x) => x.isEven);

  // ResultA: 4
  // ResultB: 2
}

Implementation

int count([bool Function(T element)? condition]) {
  if (condition == null) return length;

  var count = 0;
  for (var v in this) {
    if (condition(v)) {
      count++;
    }
  }

  return count;
}