count method

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

Return a number of the existing elements by a specific predicate example: final aboveTwenty = User(33, "chicko"), User(45, "ronit"), User(19, "amsalam"), .count((user) => user.age > 20); // 2

Implementation

int count([bool predicate(T element)?]) {
  var count = 0;
  if (predicate == null) {
    return length;
  } else {
    for (var current in this) {
      if (predicate(current)) {
        count++;
      }
    }
  }

  return count;
}