# singleWhere method

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