第五条：用枚举表示状态、选项、状态码

简单枚举类型

enum EOCConnectionState {
    EOCConnectionStateDisconnected,
    EOCConnectionStateConnecting,
    EOCConnectionStateConnected,
}
typedef enum EOCConnectionState EOCConnectionState;

这样就可以简写的EOCConnectionState来代替完整的enum EOCConnectionState。

指定底层数据类型

enum EOCConnectionState : NSInteger {/* ... */}

或者向前声明：

enum EOCConnectionState : NSInteger;

彼此组合的枚举

各选项之间可以通过”按位或操作符”。

enum UIViewAutoresizing {
    UIViewAutoresizingNone = 0,
    UIViewAutoresizingFlexibleLeftMargin = 1 << 0,
    UIViewAutoresizingFlexibleWidth = 1 << 1,
    UIViewAutoresizingFlexibleRightMargin = 1 << 2,
    UIViewAutoresizingFlexibleTopMargin = 1 << 3,
    ...
}

Foundation框架辅助宏

这些宏具有向后兼容能力。

typedef NS_ENUM(NSUInteger, EOCConnectionState) {
    EOConnectionStateDisconnected,
    ...
}

typedef NS_OPTIONS(NSUInteger, EOCPermittedDirection) {
    EOCPermittedDirectionUp = 1 << 0,
    ...
}

用枚举定义定义状态机，最好不要有default分支。

switch(_currentState) {
    case EOCConnectionStateDisconnected:
        break;
    case EOCConnectionStateConnecting:
        break;
    case EOCConnectionStateConnected:
        break;
}