RAC中的reduceEach

前面可以看到RAC中的zip和combineLatest最后都会走到reduceEach，这个RACStream中的方法，来看源码：

- (instancetype)reduceEach:(id (^)())reduceBlock {
    NSCParameterAssert(reduceBlock != nil);

    __weak RACStream *stream __attribute__((unused)) = self;
    return [[self map:^(RACTuple *t) {
        NSCAssert([t isKindOfClass:RACTuple.class], @"Value from stream %@ is not a tuple: %@", stream, t);
        return [RACBlockTrampoline invokeBlock:reduceBlock withArguments:t];
    }] setNameWithFormat:@"[%@] -reduceEach:", self.name];
}

打了断言就是数据类型必须封装为RACTuple，核心代码为RACBlockTrampoline：

//初始化，没啥说的
- (id)initWithBlock:(id)block {
    self = [super init];
    if (self == nil) return nil;

    _block = [block copy];

    return self;
}

+ (id)invokeBlock:(id)block withArguments:(RACTuple *)arguments {
    NSCParameterAssert(block != NULL);

    RACBlockTrampoline *trampoline = [[self alloc] initWithBlock:block];
    return [trampoline invokeWithArguments:arguments];
}

- (id)invokeWithArguments:(RACTuple *)arguments {
//根据RACTuple的个数选择selector，最多支持15个，也就是你combineLatest最多只能有15个信号
    SEL selector = [self selectorForArgumentCount:arguments.count];
//NSInvocation可以单纯的理解为执行一个方法，比performSelector强大，因为他可以带很多参数进去
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:[self methodSignatureForSelector:selector]];
    invocation.selector = selector;
    invocation.target = self;

    for (NSUInteger i = 0; i < arguments.count; i++) {
//把参数带进去
        id arg = arguments[i];
        NSInteger argIndex = (NSInteger)(i + 2);
        [invocation setArgument:&arg atIndex:argIndex];
    }

    [invocation invoke];
    
    __unsafe_unretained id returnVal;
    [invocation getReturnValue:&returnVal];
    return returnVal;
}
//写法不漂亮，也是无奈之举
- (SEL)selectorForArgumentCount:(NSUInteger)count {
    NSCParameterAssert(count > 0);

    switch (count) {
        case 0: return NULL;
        case 1: return @selector(performWith:);
        case 2: return @selector(performWith::);
        case 3: return @selector(performWith:::);
        case 4: return @selector(performWith::::);
        case 5: return @selector(performWith:::::);
        case 6: return @selector(performWith::::::);
        case 7: return @selector(performWith:::::::);
        case 8: return @selector(performWith::::::::);
        case 9: return @selector(performWith:::::::::);
        case 10: return @selector(performWith::::::::::);
        case 11: return @selector(performWith:::::::::::);
        case 12: return @selector(performWith::::::::::::);
        case 13: return @selector(performWith:::::::::::::);
        case 14: return @selector(performWith::::::::::::::);
        case 15: return @selector(performWith:::::::::::::::);
    }

    NSCAssert(NO, @"The argument count is too damn high! Only blocks of up to 15 arguments are currently supported.");
    return NULL;
}

- (id)performWith:(id)obj1 {
    id (^block)(id) = self.block;
    return block(obj1);
}

- (id)performWith:(id)obj1 :(id)obj2 {
    id (^block)(id, id) = self.block;
    return block(obj1, obj2);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 {
    id (^block)(id, id, id) = self.block;
    return block(obj1, obj2, obj3);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 :(id)obj4 {
    id (^block)(id, id, id, id) = self.block;
    return block(obj1, obj2, obj3, obj4);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 :(id)obj4 :(id)obj5 {
    id (^block)(id, id, id, id, id) = self.block;
    return block(obj1, obj2, obj3, obj4, obj5);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 :(id)obj4 :(id)obj5 :(id)obj6 {
    id (^block)(id, id, id, id, id, id) = self.block;
    return block(obj1, obj2, obj3, obj4, obj5, obj6);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 :(id)obj4 :(id)obj5 :(id)obj6 :(id)obj7 {
    id (^block)(id, id, id, id, id, id, id) = self.block;
    return block(obj1, obj2, obj3, obj4, obj5, obj6, obj7);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 :(id)obj4 :(id)obj5 :(id)obj6 :(id)obj7 :(id)obj8 {
    id (^block)(id, id, id, id, id, id, id, id) = self.block;
    return block(obj1, obj2, obj3, obj4, obj5, obj6, obj7, obj8);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 :(id)obj4 :(id)obj5 :(id)obj6 :(id)obj7 :(id)obj8 :(id)obj9 {
    id (^block)(id, id, id, id, id, id, id, id, id) = self.block;
    return block(obj1, obj2, obj3, obj4, obj5, obj6, obj7, obj8, obj9);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 :(id)obj4 :(id)obj5 :(id)obj6 :(id)obj7 :(id)obj8 :(id)obj9 :(id)obj10 {
    id (^block)(id, id, id, id, id, id, id, id, id, id) = self.block;
    return block(obj1, obj2, obj3, obj4, obj5, obj6, obj7, obj8, obj9, obj10);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 :(id)obj4 :(id)obj5 :(id)obj6 :(id)obj7 :(id)obj8 :(id)obj9 :(id)obj10 :(id)obj11 {
    id (^block)(id, id, id, id, id, id, id, id, id, id, id) = self.block;
    return block(obj1, obj2, obj3, obj4, obj5, obj6, obj7, obj8, obj9, obj10, obj11);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 :(id)obj4 :(id)obj5 :(id)obj6 :(id)obj7 :(id)obj8 :(id)obj9 :(id)obj10 :(id)obj11 :(id)obj12 {
    id (^block)(id, id, id, id, id, id, id, id, id, id, id, id) = self.block;
    return block(obj1, obj2, obj3, obj4, obj5, obj6, obj7, obj8, obj9, obj10, obj11, obj12);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 :(id)obj4 :(id)obj5 :(id)obj6 :(id)obj7 :(id)obj8 :(id)obj9 :(id)obj10 :(id)obj11 :(id)obj12 :(id)obj13 {
    id (^block)(id, id, id, id, id, id, id, id, id, id, id, id, id) = self.block;
    return block(obj1, obj2, obj3, obj4, obj5, obj6, obj7, obj8, obj9, obj10, obj11, obj12, obj13);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 :(id)obj4 :(id)obj5 :(id)obj6 :(id)obj7 :(id)obj8 :(id)obj9 :(id)obj10 :(id)obj11 :(id)obj12 :(id)obj13 :(id)obj14 {
    id (^block)(id, id, id, id, id, id, id, id, id, id, id, id, id, id) = self.block;
    return block(obj1, obj2, obj3, obj4, obj5, obj6, obj7, obj8, obj9, obj10, obj11, obj12, obj13, obj14);
}

- (id)performWith:(id)obj1 :(id)obj2 :(id)obj3 :(id)obj4 :(id)obj5 :(id)obj6 :(id)obj7 :(id)obj8 :(id)obj9 :(id)obj10 :(id)obj11 :(id)obj12 :(id)obj13 :(id)obj14 :(id)obj15 {
    id (^block)(id, id, id, id, id, id, id, id, id, id, id, id, id, id, id) = self.block;
    return block(obj1, obj2, obj3, obj4, obj5, obj6, obj7, obj8, obj9, obj10, obj11, obj12, obj13, obj14, obj15);
}