枚举

https://blog.csdn.net/daleiwang/article/details/50581872

1.iOS程序中，最好所有的枚举都用“NS_ENUM”和“NS_OPTIONS”定义，保证统一。

    //NS_ENUM，定义状态等普通枚举
    typedef NS_ENUM(NSUInteger, TTGState) {
        TTGStateOK = 0,
        TTGStateError,
        TTGStateUnknow
    };
     
    //NS_OPTIONS，定义选项
    typedef NS_OPTIONS(NSUInteger, TTGDirection) {
        TTGDirectionNone = 0,
        TTGDirectionTop = 1 << 0,
        TTGDirectionLeft = 1 << 1,
        TTGDirectionRight = 1 << 2,
        TTGDirectionBottom = 1 << 3
    };

2.熟悉一下位运算
https://www.jianshu.com/p/66bae556483d