# singleWhere method

E singleWhere (bool test(E value), { E orElse() })

Returns 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. Otherwise, if there are no matching elements, or if there is more than one matching element, the result of invoking the `orElse` function is returned. If `orElse` is omitted, it defaults to throwing a StateError.

## Implementation

    E singleWhere(bool test(E value), {E orElse()}) {
      E result = null;
      bool foundMatching = false;
      for (E element in this) {
        if (test(element)) {
          if (foundMatching) {
            throw IterableElementError.tooMany();
          }
          result = element;
          foundMatching = true;
        }
      }
      if (foundMatching) return result;
      if (orElse != null) return orElse();
      throw IterableElementError.noElement();
    }