/// Creates a type-erased collection that wraps the given collection.
    ///
    /// - Parameter base: The collection to wrap.
    ///
    /// - Complexity: O(1).
    public init<C : BidirectionalCollection where C.Iterator.Element == Element, C.SubSequence : BidirectionalCollection, C.SubSequence.Iterator.Element == Element, C.SubSequence.Index == C.Index, C.SubSequence.Indices : BidirectionalCollection, C.SubSequence.Indices.Iterator.Element == C.Index, C.SubSequence.Indices.Index == C.Index, C.SubSequence.Indices.SubSequence == C.SubSequence.Indices, C.SubSequence.SubSequence == C.SubSequence, C.Indices : BidirectionalCollection, C.Indices.Iterator.Element == C.Index, C.Indices.Index == C.Index, C.Indices.SubSequence == C.Indices>(_ base: C)

  public init<C : ${SubProtocol}>(_ base: C)
    where
    C.Iterator.Element == Element,

    // FIXME(ABI)#101 (Associated Types with where clauses): these constraints should be applied to
    // associated types of Collection.
    C.SubSequence : ${SubProtocol},
    C.SubSequence.Iterator.Element == Element,
    C.SubSequence.Index == C.Index,
    C.SubSequence.Indices : ${SubProtocol},
    C.SubSequence.Indices.Iterator.Element == C.Index,
    C.SubSequence.Indices.Index == C.Index,
    C.SubSequence.Indices.SubSequence == C.SubSequence.Indices,
    C.SubSequence.SubSequence == C.SubSequence,
    C.Indices : ${SubProtocol},
    C.Indices.Iterator.Element == C.Index,
    C.Indices.Index == C.Index,
    C.Indices.SubSequence == C.Indices {
    // Traversal: ${Traversal}
    // SubTraversal: ${SubTraversal}
    self._box = _${SubProtocol}Box<C>(
      _base: base)
  }