add FISetter (#6)

Sources/fluentinterface/FluentInterface.swift

@@ -26,6 +26,9 @@ public postfix func - <T>(lhs: FluentInterface<T>) -> T {
 /// ```
 /// resource  https://www.appcoda.com.tw/fluent-interface/
 @dynamicMemberLookup public struct FluentInterface<Subject> {
+
+  public typealias FISetter<Value> = ((Value) -> FluentInterface<Subject>)
+
   let subject: Subject
 
   // 因為要動到 subject 的屬性，所以 keyPath 的型別必須是 WritableKeyPath
@@ -43,20 +46,20 @@ public postfix func - <T>(lhs: FluentInterface<T>) -> T {
   /// [Flentinterface] get the subject.
   public func unwrappingSubject() -> Subject {
     subject
-	}
-	/// [Fluentinterface] Quick way to touch subject and remain fluent interface
-	/// - Parameter handlel: A cloure to get the subject
-	public nonmutating func handlingSubject(_ handle:
-		(Subject) -> Void) -> Self {
-		handle(subject)
-		return self
-	}
-	/// [Fluentinterface] Quick way to manipulate subject and remain fluent interface
-	/// - Parameter handle: A cloure to inout set subject
-	public nonmutating func manipulateSubjct(_ handle:
-		(inout Subject) -> Void) -> Self {
-		var subject = self.subject
-		handle(&subject)
-		return FluentInterface(subject: subject)
-	}
+  }
+  /// [Fluentinterface] Quick way to touch subject and remain fluent interface
+  /// - Parameter handlel: A cloure to get the subject
+  public nonmutating func handlingSubject(_ handle:
+    (Subject) -> Void) -> Self {
+    handle(subject)
+    return self
+  }
+  /// [Fluentinterface] Quick way to manipulate subject and remain fluent interface
+  /// - Parameter handle: A cloure to inout set subject
+  public nonmutating func manipulateSubjct(_ handle:
+    (inout Subject) -> Void) -> Self {
+    var subject = self.subject
+    handle(&subject)
+    return FluentInterface(subject: subject)
+  }
 }