Swift Enumeration（斯威夫特枚举）

Swift Enumeration（斯威夫特枚举）

目录：
1、Enumeration Syntax（枚举语法）
2、Matching Enumeration value with a switch statement（使用switch语法枚举值）
3、Iterating over Enumeration cases（迭代枚举实例）
4、Associated values（关联值）
5、Raw Values（原始值）
6、Recursive Enumeration（递归枚举）

1、Enumeration Syntax（枚举语法）

Keyword:
enum define enum class
case define enum variable

/*
 Define class of enum type.
 */
enum DayWeek{
    
    case Sunday
    case Monday
    case Tuesday
    case Wendensday
    case Thursday
    case Friday
    case Saturday
    
}

2、Matching Enumeration value with a switch statement（使用switch语法枚举值）

/*
 Define class of enum type.
 */
enum DayWeek{
    
    case Sunday
    case Monday
    case Tuesday
    case Wendensday
    case Thursday
    case Friday
    case Saturday
    
}

/*
 Using switch to match enum type.
 */
var weekDay = DayWeek.Friday

switch  weekDay{
    case .Monday://be equal to DayWeek.Monday
        print("Monday")
    case .Friday://be equal to DayWeek.Friday
        print("Friday")
    default:
        print("unknown")
}

3、Iterating over Enumeration cases（迭代枚举实例）

:CaseIterable 启用拥有该枚举的所有实例的集合
并，将所有实例的集合作为枚举类型的allCases属性公开

/*
 Define class of enum type.
 */
enum DayWeek : CaseIterable{
    
    case Sunday
    case Monday
    case Tuesday
    case Wendensday
    case Thursday
    case Friday
    case Saturday
    
}


print("enum size:\(DayWeek.allCases.count)")//enum size:7

/*
 Iterate collection of enum.
 */
for value in DayWeek.allCases{
    print("DayWeek vlaue:\(value)")
}

4、Associated values（关联值）

/*
 Define enum type's class
 */
enum Barcode{
    case productOne(Int,Int)
    case qrCode(String)
    
    case Friday
}

var productBarcode = Barcode.productOne(8, 8)

productBarcode = Barcode.qrCode("ABCDEFGHIJKLMNOPQRSTUVWXYZ")

//switch expression
switch productBarcode {
    case .productOne(let one,  let two)://let two never used ,let two equal to _
        print("product:\(one)")
    case .qrCode(let name):
        print("qrCode:\(name)")
    default:
        print("unknown")
}

/*
 print :qrCode:ABCDEFGHIJKLMNOPQRSTUVWXYZ
 */

上面可简洁/省略的代码，如下

未省略/简洁

//switch expression
switch productBarcode {
    case .productOne(let one,  let two)://let two never used ,let two equal to _
        print("product:\(one)")
    case .qrCode(let name):
        print("qrCode:\(name)")
    default:
        print("unknown")
}

省略/简洁

//switch expression
switch productBarcode {
    case let .productOne(one,two)://let two never used ,let two equal to _
        print("product:\(one)")
    case let .qrCode(name):
        print("qrCode:\(name)")
    default:
        print("unknown")
}

5、Raw Values（原始值）

原始值也称为默认值

/*
 Enum default variable value.
 */

enum EnumDefaultValue: Int{

    case one = 1
    case two = 2
    

}
print("enum one value:\(EnumDefaultValue.one)")//enum one values:one
print("enum one's rawValue:\(EnumDefaultValue.one.rawValue)")//enum one's rawValue:1

6、Recursive Enumeration（递归枚举）

定义可递归的枚举（indirect）

enum Expression{
    
    case number(Int)
    
    indirect case addition(Expression,Expression)
    
    indirect case multiplication(Expression, Expression)
}

func evaluate(_ expression:Expression) -> Int{
    
    switch expression {
    case let .number(value):
        return value
    case let .addition(one, two):
        return (evaluate(one) + evaluate(two))
    case let .multiplication(one, two):
        return (evaluate(one) * evaluate(two))
    default:
        return -1;
    }
}

var expressionNumber = Expression.number(5)
print("evaluate:\(evaluate(expressionNumber))")//evaluate:5

var expressionVar = Expression.addition(expressionNumber, expressionNumber)
print("evaluate:\(evaluate(expressionVar))")//evaluate:10

expressionVar = Expression.multiplication(expressionNumber, expressionNumber)
print("evaluate:\(evaluate(expressionVar))")//evaluate:25

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未完待续。。。