# 4/7 (四) 基本資料類別

|Swift|Kotlin|
|---|---|
|struct| data class |
|class| class|
| x | abstract class |
|protocol| interface = abstrat class|
|enum| enum class = sealed class |
|optional| x |
|!| lateinit
| | !! (nonNull)|

補充：
https://docs.swift.org/swift-book/LanguageGuide/TheBasics.html

struct <---- value type
class <---- referenece type

### 常數變數

let pi = 3.14
var num = 123
pi = 345 // 不行 
num = 456 // 可以

- 變數可以分為 get & set / get only
- get only 有個名字，叫 computed variable

### 基本的 class 這樣宣告

class KKSAVPlayer : NSObject {
    var state: KKSAVPlayerState
    var player: AVPlayer!
    var playerLayer: AVPlayerLayer!
    var masterPlaylist: ManifestMasterPlaylist?
    var duration: TimeInterval
    var currentTime: TimeInterval
}

KKSAVPlayer 繼承 NSObject

### protocol

* protocol 等於 Java 的 Interface
* Swift 的 protocol 可以繼承 protocol
* extension protocol 可以有預設的實作

protocol AppEnvProtocol {
    var castApplicationId: String { get }
    var envName: String { get }
}
struct DevelopEnv: AppEnvProtocol {
    var castApplicationId: String { return "F26E7D83" }
    var envName: String { return EnvName.develop.rawValue }
}
struct ReleaseEnv: AppEnvProtocol {
    var castApplicationId: String { return "DC01DFFB" }
    var envName: String { return EnvName.release.rawValue }
}
struct MasterEnv: AppEnvProtocol {
    var castApplicationId: String { return "365A05A2" }
    var envName: String { return EnvName.master.rawValue }
}

### enum

enum APIError {
    case none
    case specifyArgumentNotFound
    case internalServerError
    case unauthorizedToPlay
    case reachTheDeviceLimit
}

let error: APIError = .reachTheDeviceLimit