singleOrDefault method

T singleOrDefault({ required T defaultValue, })

Returns the single element in the iterable, or a defaultValue if no such element exists.

Returns the single value in this iterable, assuming the iterable has a length of one. If the iterable is empty, the value specified by defaultValue is returned instead. If the iterable contains more than one element, a StateError is thrown.

This method function will short-circuit after reaching the second element of the iteration, if one exists. In the worst-case scenario, this method will iterate over two elements of the iterable.

Example:

void main() {
  final list = [];
  final result = list.singleOrDefault(defaultValue: -1);

  // Result: -1
}

Implementation

T singleOrDefault({required T defaultValue}) {
  final iter = iterator;
  if (!iter.moveNext()) return defaultValue;

  var val = iter.current;
  if (iter.moveNext()) {
    throw StateError('The iterable has more than one element.');
  }

  return val;
}