《Effective Objective-C 2.0》学习笔记1

//eg1：
#define ANIMATION_DURATION 0.3  //没有类型信息，所有的ANIMATION_DURATION都会被替换
//解决办法
static const NSTimeInterval kAnimationDuration = 0.3;
//eg2：
//声明全局通知名称
//in the header file
extern NSString *const NOTIFACATION;
//in the implementation file
NSString *const NOTIFACATION = @"NOTIFACATION";

//定义枚举（指明底层数据类型）
enum State : NSInteger {
Eg1 = 0,
Eg2 = 1 << 0,
Eg3 = 1 << 1,
Eg4 = 1 << 2,
Eg5 = 1 << 3,
Eg6 = 1 << 4,
};
typedef enum State State;