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。。。
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