RACUnarySequence作为RACSequence的子类，Unary的意思是一元的，注释Private class representing a sequence of exactly one value也说明了该类只包含一个值。
完整测试用例在这里。
看看.m中方法的作用
+ (instancetype)return:(id)value {
RACUnarySequence *sequence = [[self alloc] init];
sequence.head = value;
return [sequence setNameWithFormat:@"+return: %@", [value rac_description]];
}
重写父类的方法，返回只有一个值的序列。
测试用例：
- (void)test_return
{
RACUnarySequence *sequence = [RACUnarySequence return:@"xxx"];
NSLog(@"return -- %@", sequence);
// 打印日志：
/*
2018-08-16 17:21:03.940582+0800 TestRACUnarySequence[15973:17015192] return -- <RACUnarySequence: 0x600000238820>{ name = , head = xxx }
*/
}
- (RACSequence *)tail {
return nil;
}
返回nil。也就是说该类只有一个值。
测试用例：
- (void)test_tail
{
RACUnarySequence *sequence = [RACUnarySequence return:@[@1, @2, @3]];
NSLog(@"tail -- %@", sequence.tail);
// 打印日志：
/*
2018-08-16 17:22:49.841689+0800 TestRACUnarySequence[16078:17019928] tail -- (null)
*/
}
- (instancetype)bind:(RACStreamBindBlock (^)(void))block {
RACStreamBindBlock bindBlock = block();
BOOL stop = NO;
RACSequence *result = (id)[bindBlock(self.head, &stop) setNameWithFormat:@"[%@] -bind:", self.name];
return result ?: self.class.empty;
}
以head值为参数调用block获取一个RACSequence对象result。如果result存在，返回；如果不存在，返回空序列。
测试用例：
- (void)test_bind
{
RACUnarySequence *sequence = [RACUnarySequence return:@(1)];
RACSequence *s = [sequence bind:^RACStreamBindBlock{
return ^(id value, BOOL *stop) {
return [RACUnarySequence return:@(100)];
};
}];
NSLog(@"bind -- %@", s);
// 打印日志：
/*
2018-08-16 17:25:01.532451+0800 TestRACUnarySequence[16176:17026442] bind -- <RACUnarySequence: 0x6000002341c0>{ name = , head = 100 }
*/
}
后面的一些关于 序列化、格式化日志 的方法不再分析。
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