ReactiveCocoa中的宏2

2017-05-16 本文已影响0人林炜超

1、keypath

keypath的使用

NSString *UTF8StringPath = @keypath(str.lowercaseString.UTF8String);
// => @"lowercaseString.UTF8String"

NSString *versionPath = @keypath(NSObject, version);
// => @"version"

NSString *lowercaseStringPath = @keypath(NSString.new, lowercaseString);
// => @"lowercaseString"

调用了metamacro_argcount(详情可见ReactiveCocoa中的宏1)，得到传入参数个数

#define keypath(...) \
    metamacro_if_eq(1, metamacro_argcount(__VA_ARGS__))(keypath1(__VA_ARGS__))(keypath2(__VA_ARGS__))

metamacro_if_eq，调用了metamacro_concat(详情可见ReactiveCocoa中的宏1)，将metamacro_if_eq, A合并

#define metamacro_if_eq(A, B) \
        metamacro_concat(metamacro_if_eq, A)(B)

metamacro_if_eq1

#define metamacro_if_eq1(VALUE) metamacro_if_eq0(metamacro_dec(VALUE))

metamacro_dec

#define metamacro_dec(VAL) \
        metamacro_at(VAL, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)

metamacro_at

#define metamacro_at(N, ...) \
        metamacro_concat(metamacro_at, N)(__VA_ARGS__)

metamacro_at0-19，对应着参数个数，因为传入的20个参数是以-1开始的，所以最终得到的值是参数个数减一

#define metamacro_at0(...) metamacro_head(__VA_ARGS__)
#define metamacro_at1(_0, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at2(_0, _1, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at3(_0, _1, _2, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at4(_0, _1, _2, _3, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at5(_0, _1, _2, _3, _4, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at6(_0, _1, _2, _3, _4, _5, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at7(_0, _1, _2, _3, _4, _5, _6, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at8(_0, _1, _2, _3, _4, _5, _6, _7, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at9(_0, _1, _2, _3, _4, _5, _6, _7, _8, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at10(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at11(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at12(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at13(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at14(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at15(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at16(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at17(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at18(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at19(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, ...) metamacro_head(__VA_ARGS__)
#define metamacro_at20(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19, ...) metamacro_head(__VA_ARGS__)

metamacro_head取第一个参数

#define metamacro_head(...) \
        metamacro_head_(__VA_ARGS__, 0)

#define metamacro_head_(FIRST, ...) FIRST

metamacro_if_eq0

#define metamacro_if_eq0(VALUE) \
    metamacro_concat(metamacro_if_eq0_, VALUE)

metamacro_if_eq0_0-19
参数个数减1等于0，调用metamacro_if_eq0_0(keypath1)(keypath2)，执行keypath1，并带走keypath2(metamacro_consume_)
参数个数减1大于等于1，调用metamacro_if_eq0_x(keypath1)(keypath2)，带走keypath1，并执行keypath2(metamacro_expand_)

#define metamacro_if_eq0_0(...) __VA_ARGS__ metamacro_consume_
#define metamacro_if_eq0_1(...) metamacro_expand_
#define metamacro_if_eq0_2(...) metamacro_expand_
#define metamacro_if_eq0_3(...) metamacro_expand_
#define metamacro_if_eq0_4(...) metamacro_expand_
#define metamacro_if_eq0_5(...) metamacro_expand_
#define metamacro_if_eq0_6(...) metamacro_expand_
#define metamacro_if_eq0_7(...) metamacro_expand_
#define metamacro_if_eq0_8(...) metamacro_expand_
#define metamacro_if_eq0_9(...) metamacro_expand_
#define metamacro_if_eq0_10(...) metamacro_expand_
#define metamacro_if_eq0_11(...) metamacro_expand_
#define metamacro_if_eq0_12(...) metamacro_expand_
#define metamacro_if_eq0_13(...) metamacro_expand_
#define metamacro_if_eq0_14(...) metamacro_expand_
#define metamacro_if_eq0_15(...) metamacro_expand_
#define metamacro_if_eq0_16(...) metamacro_expand_
#define metamacro_if_eq0_17(...) metamacro_expand_
#define metamacro_if_eq0_18(...) metamacro_expand_
#define metamacro_if_eq0_19(...) metamacro_expand_
#define metamacro_if_eq0_20(...) metamacro_expand_

metamacro_consume_

#define metamacro_consume_(...)

metamacro_expand_

#define metamacro_expand_(...) __VA_ARGS__

keypath1，逗号表达式可以取后值，但前面的值表达式照样运算，可以用void忽略编译器警告
#PATH：C字符串，#PATH首次出现'.'的位置加1
前面NO&&NO的含义：编译器知道在NO后且什么的结果都是NO，于是后面的语句被优化掉了。也就是说keypath宏中这个NO && ((void)OBJ.PATH, NO)就使得在编译后后面的部分不出现在最后的代码中，于是乎既实现了keypath的自动提示功能，又保证编译后不执行多余的代码
详情可见链接最后一段带自动提示的keypath宏

#define keypath1(PATH) \
    (((void)(NO && ((void)PATH, NO)), strchr(# PATH, '.') + 1))

keypath2

#define keypath2(OBJ, PATH) \
    (((void)(NO && ((void)OBJ.PATH, NO)), # PATH))

2、collectionKeypath

collectionKeypath的使用

 NSString *employessFirstNamePath = @collectionKeypath(department.employees, Employee.new, firstName)
 // => @"employees.firstName"
 
 NSString *employessFirstNamePath = @collectionKeypath(Department.new, employees, Employee.new, firstName)
 // => @"employees.firstName"

collectionKeypath

#define collectionKeypath(...) \
    metamacro_if_eq(3, metamacro_argcount(__VA_ARGS__))(collectionKeypath3(__VA_ARGS__))(collectionKeypath4(__VA_ARGS__))

metamacro_if_eq

#define metamacro_if_eq(A, B) \
        metamacro_concat(metamacro_if_eq, A)(B

参数个数减3等于0，#define metamacro_if_eq0_0(...) __VA_ARGS__ metamacro_consume_，执行collectionKeypath3
参数个数减3大于等于1，metamacro_expand_，执行collectionKeypath4

#define metamacro_if_eq1(VALUE) metamacro_if_eq0(metamacro_dec(VALUE))
#define metamacro_if_eq2(VALUE) metamacro_if_eq1(metamacro_dec(VALUE))
#define metamacro_if_eq3(VALUE) metamacro_if_eq2(metamacro_dec(VALUE))

#define collectionKeypath3(PATH, COLLECTION_OBJECT, COLLECTION_PATH) ([[NSString stringWithFormat:@"%s.%s",keypath(PATH), keypath(COLLECTION_OBJECT, COLLECTION_PATH)] UTF8String])

#define collectionKeypath4(OBJ, PATH, COLLECTION_OBJECT, COLLECTION_PATH) ([[NSString stringWithFormat:@"%s.%s",keypath(OBJ, PATH), keypath(COLLECTION_OBJECT, COLLECTION_PATH)] UTF8String])

ReactiveCocoa中的宏2

1、keypath

2、collectionKeypath

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