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 and the underlying collection extends or implements EfficientLengthIterable, the count method will call the length property of the iterable as an O(1) operation. Otherwise, the count function will iterate over every element in the iterable.

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]) {
  checkNullError(this);
  if (condition == null) return length;

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

  return count;
}