Added helpers to Failable<Optional<T>, V> type

Sources/Validation/Failable+Helpers/Failable+Optional.swift

@@ -0,0 +1,36 @@
+extension Failable {
+    
+    /// See [`Optional.map(_:)`](https://developer.apple.com/documentation/swift/optional/1539476-map).
+    public func map<U, Wrapped>(_ transform: (Wrapped) throws -> U) rethrows -> U? where T == Optional<Wrapped> {
+        return try self.value.map(transform)
+    }
+    
+    /// See [`Optional.flatMap(_:)`](https://developer.apple.com/documentation/swift/optional/1540500-flatmap).
+    public func flatMap<U, Wrapped>(_ transform: (Wrapped) throws -> U?) rethrows -> U? where T == Optional<Wrapped> {
+        return try self.value.flatMap(transform)
+    }
+    
+    /// See [`Optional.==(_:_:)`](https://developer.apple.com/documentation/swift/optional/2950146).
+    public static func == <Wrapped>(lhs: Failable<Wrapped?, Validations>, rhs: Failable<Wrapped?, Validations>)
+        -> Bool where T == Optional<Wrapped>, Wrapped: Equatable
+    {
+        return lhs.value == rhs.value
+    }
+    
+    /// See [`Optional.!=(_:_:)`](https://developer.apple.com/documentation/swift/optional/2949565).
+    public static func != <Wrapped>(lhs: Failable<Wrapped?, Validations>, rhs: Failable<Wrapped?, Validations>)
+        -> Bool where T == Optional<Wrapped>, Wrapped: Equatable
+    {
+        return lhs.value != rhs.value
+    }
+}
+
+/// See [`Optional.??(_:_:)`](https://developer.apple.com/documentation/swift/1539917).
+public func ?? <T, V>(optional: Failable<T?, V>, defaultValue: @autoclosure () throws -> T) rethrows -> T {
+    return try optional.value ?? defaultValue
+}
+
+/// See [`Optional.??(_:_:)`](https://developer.apple.com/documentation/swift/1541015).
+public func ?? <T, V>(optional: Failable<T?, V>, defaultValue: @autoclosure () throws -> T?) rethrows -> T? {
+    return try optional.value ?? defaultValue
+}