one method

bool one(
  1. bool test(
    1. E
    )
)

Returns true if there is exactly one element of this which satisfies test.

Example:

[1, 2, 3].one((e) => e == 2); // 1 element satisfies. Returns true.
[1, 2, 3].one((e) => e > 4); // No element satisfies. Returns false.
[1, 2, 3].one((e) => e > 1); // >1 element satisfies. Returns false.

Implementation

bool one(bool Function(E) test) {
  bool foundOne = false;
  for (var e in this) {
    if (test(e)) {
      if (foundOne) return false;
      foundOne = true;
    }
  }
  return foundOne;
}