dart:collection

length property

int length

Returns the number of elements in this.

Counting all elements may involve iterating through all elements and can therefore be slow. Some iterables have a more efficient way to find the number of elements.

Source

int get length {
  assert(this is! EfficientLengthIterable);
  int count = 0;
  Iterator it = iterator;
  while (it.moveNext()) {
    count++;
  }
  return count;
}