一、关联值为泛型类型

 enum Result1<Success, Failure>{
   case success(Success),failure(Failure)
}

enum Result2<Success>{

  case success(Success),  failure(String)
}


enum Result3<Failure>{

  case success(Int), failure(Failure) 
}

 let result1 =  Result1<Int,String>.success(1)
 let result2 =  Result2<Int>.success(1) 
 let result3 =  Result3.failure(4)

在以上的例子中，关联值是为Success或Failure类型，而Success或Failure类型是声明的一个泛型类型，所以当你要给枚举的成员变量的关联值存储一个值时，你就需要先去告诉枚举此时真实需要的是什么类型。例如：Result1<Int,String>就告诉，此时Success是Int类型，Failure是String。当然像 let result3 = Result3.failure(4)，可以让编译器自动推断处是Int时，就可以省略。

二、在闭包中的使用

闭包表达式

 enum Result1<Success, Failure>{
   case success(Success),failure(Failure)
}

    let fn = { (v1:Result1<Int,Int>) -> () in
            switch v1 {
                  case .success(let a):  print(a)
                  case  let .failure(b):  print(b)
            }
        }
            
        let fn1 = { (v1:Result1<Int,String>) -> () in
            switch v1 {
                  case .success(_):  print("测试")
                  case  .failure(_):  print("测试")
            }
        }
       
        let fn2 = { (v1:Result1<String,String>) -> () in
            print("测试")
        }
        fn(Result1<Int,Int>.success(1))
        fn1(Result1<Int,String>.failure("fff"))
        fn2(Result1<String,String>.failure("hhh"))

闭包作为参数类型

 enum Result1<Success, Failure>{
   case success(Success),failure(Failure)
}

func exec(fn: (Result1<Int,Int>) -> ()) {
        fn(Result1.success(200))
        fn(Result1.failure(12))
    }
    
    func exec1(fn: (Result1<String,Int>) -> ()) {
        fn(Result1.success("成功"))
        fn(Result1.failure(12))
    }
    
    exec{ (result:Result1<Int,Int>) in
                switch result{
                case .success(let a) :print(a)
                case .failure(let b):print(b)
               }
        }
        
        exec1 { response in
            switch response{
            case .success(let a) :print(a)
            case .failure(let b):print(b)
           }
        }

三、Swift 5之Result类型

https://www.jianshu.com/p/78ad789577df
https://www.jianshu.com/p/a3712edc9367

public enum Result<Success, Failure> where Failure : Error{
    case success(Success)
    case failure(Failure)
}

很显然Result类型就是枚举的泛性在闭包中使用的最大实践