Swift中Enum的使用姿势

Swift的Enum类型可以存储值

<pre>
enum iOSDeviceSystemType {
case iPhone(String)
case iPad(String)
case iWatch
}

var myDeviceSystem = iOSDeviceSystemType.iPad("9.1")

switch myDeviceSystem {
case .iPhone(let model):
print("My iPhone's System is (model)");
break
case .iPad(let model) :
print("My iPad's System is (model)");
break
case .iWatch: print("I had no iWatch, 😄😄😄")
default:
print("not an iOS device")
}
</pre>

比较两个枚举值是否相等

<pre>
var newDevice = iOSDeviceSystemType.iPhone("9.1")
var oldDevice = iOSDeviceSystemType.iPhone("8.1")

newDevice == oldDevice
</pre>

系统提示：

Binary operator '==' cannot be applied to two 'iOSDeviceSystemType' operands

总结：在Swift中，enum不提供 == 运算符的操作。

正确姿势：

使用switch去判断类型

<pre>
var newDevice = iOSDeviceSystemType.iPhone("9.1")
var oldDevice = iOSDeviceSystemType.iPhone("8.1")

func sameDevice(firstDevice: iOSDeviceSystemType, secondDevice: iOSDeviceSystemType) -> Bool {

switch (firstDevice, secondDevice) {
    
case(.iPhone(let a), .iPhone(let b)) where a == b : return true

case(.iPad(let a), .iPhone(let b)) where a == b : return true

case (.iWatch, .iWatch):
    return true

default:
    return false
}

}

print(sameDevice(myDeviceSystem, secondDevice: oldDevice))
</pre>

默认值

<pre>
enum Direction: Int {
case Up = 1
case Down
case Left
case Right
}
</pre>

使用Row Value创建枚举

<pre>
var direction = Direction(rawValue: 4)
</pre>

提示: rawValue返回的值，是Optional类型。上述例子返回的是Direction?，并不是Direction类型。

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提示：有时候，点语法不太友好，虽然说姿势最佳的是使用点语法，但是编译器会卡顿，并且不提示，如果没耐心，还是全写来的方便。

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