description

# singleWhere method

E singleWhere(

1. bool test(
   1. E element
   ), {
2. E orElse()?,

})
inherited

The single element that satisfies `test`.

Checks elements to see if `test(element)` returns true. If exactly one element satisfies `test`, that element is returned. If more than one matching element is found, throws StateError. If no matching element is found, returns the result of `orElse`. If `orElse` is omitted, it defaults to throwing a StateError.

Example:

    final numbers = <int>[2, 2, 10];
    var result = numbers.singleWhere((element) => element > 5); // 10

When no matching element is found, the result of calling `orElse` is returned instead.

    result = numbers.singleWhere((element) => element == 1,
        orElse: () => -1); // -1

There must not be more than one matching element.

    result = numbers.singleWhere((element) => element == 2); // Throws Error.

## Implementation

    E singleWhere(bool test(E element), {E Function()? orElse}) {
      int length = this.length;
      late E match;
      bool matchFound = false;
      for (int i = 0; i < length; i++) {
        E element = elementAt(i);
        if (test(element)) {
          if (matchFound) {
            throw IterableElementError.tooMany();
          }
          matchFound = true;
          match = element;
        }
        if (length != this.length) {
          throw ConcurrentModificationError(this);
        }
      }
      if (matchFound) return match;
      if (orElse != null) return orElse();
      throw IterableElementError.noElement();
    }