add feature manipulateSubjct (#5)

* add handlingSubject method

* add doc for handlingSubject

* add manipulatesubject

* add test case

Sources/fluentinterface/FluentInterface.swift

@@ -43,5 +43,20 @@ 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)
+	}
 }

Tests/FluentInterfaceTests/FluentinterfaceHandlerTests.swift

@@ -0,0 +1,36 @@
+import FluentInterface
+import XCTest
+
+class FluentinterfaceHandlerTests: XCTestCase {
+
+	func testHandlingSubject() {
+		class TestTarget {
+			var int:Int = 1
+			func doubleIt() {
+				int *= 2
+			}
+		}
+		let target = TestTarget()+
+			.handlingSubject{$0.doubleIt()}
+		.unwrappingSubject()
+
+		XCTAssertEqual(target.int, 2)
+	}
+	func testManipulateSubjct() {
+		struct TestTarget {
+			var int:Int = 1
+			mutating func doubleIt() {
+				int *= 2
+			}
+		}
+		let target = TestTarget()+
+			.manipulateSubjct{$0.doubleIt()}
+		.unwrappingSubject()
+
+		XCTAssertEqual(target.int, 2)
+	}
+	static var allTests = [
+		("testHandlingSubject", testHandlingSubject),
+		("testManipulateSubjct",testManipulateSubjct),
+	]
+}

Tests/FluentInterfaceTests/fluentinterfaceTests.swift

@@ -0,0 +1,8 @@
+//
+//  File.swift
+//  
+//
+//  Created by 游宗諭 on 2020/3/3.
+//
+
+import Foundation