     // ======================================================= //
     
     /// The backing storage for the ordered keys.
-    fileprivate var _orderedKeys = [Key]()
+    fileprivate var _orderedKeys: [Key]
     
     /// The backing storage for the mapping of keys to values.
-    fileprivate var _keysToValues = [Key: Value]()
+    fileprivate var _keysToValues: [Key: Value]
     
 }
 

        areInIncreasingOrder: (Element, Element) throws -> Bool
    ) rethrows {
        let keysAndValues = try Array(unsorted).sorted(by: areInIncreasingOrder)
        self.init(uniqueKeysWithValues: keysAndValues)
    }
    
    /// Initializes an ordered dictionary from a sequence of values keyed by a unique key extracted

    // ======================================================= //
    
    /// Initializes an empty ordered dictionary.
    public init() {
        self._orderedKeys = [Key]()
        self._keysToValues = [Key: Value]()
    }
    
    /// Initializes an empty ordered dictionary with preallocated space for at least the specified
    /// number of elements.
    public init(minimumCapacity: Int) {
        self.init()
        self.reserveCapacity(minimumCapacity)
    }
    
    /// Initializes an ordered dictionary from a regular unsorted dictionary by sorting it using
    /// the given sort function.
    ///
    /// - Parameter unsorted: The unsorted dictionary.
