RACSequence分析（十）—— RACEagerSequence

RACEagerSequence作为RACArraySequence的子类，顾名思义，就是热序列。想要知道与冷序列的区别，就看看.m中的方法是如何实现的。

完整测试用例在这里。

---

+ (instancetype)return:(id)value {
    return [[self sequenceWithArray:@[ value ] offset:0] setNameWithFormat:@"+return: %@", [value rac_description]];
}

重写了return:方法，通过调用sequenceWithArray:offset:获取一个对象。

测试用例：

- (void)test_return
{
    RACEagerSequence *sequence = [RACEagerSequence return:@"x"];
    NSLog(@"return -- %@", sequence);

    // 打印日志：
    /*
     2018-08-17 17:50:07.949142+0800 TestRACEagerSequence[53369:18425363] return -- <RACEagerSequence: 0x604000223700>{ name = , array = (
     x
     ) }
     */
}

---

- (instancetype)bind:(RACStreamBindBlock (^)(void))block {
    NSCParameterAssert(block != nil);
    RACStreamBindBlock bindBlock = block();
    NSArray *currentArray = self.array;
    NSMutableArray *resultArray = [NSMutableArray arrayWithCapacity:currentArray.count];

    for (id value in currentArray) {
        BOOL stop = NO;
        RACSequence *boundValue = (id)bindBlock(value, &stop);
        if (boundValue == nil) break;

        for (id x in boundValue) {
            [resultArray addObject:x];
        }

        if (stop) break;
    }

    return [[self.class sequenceWithArray:resultArray offset:0] setNameWithFormat:@"[%@] -bind:", self.name];
}

重写bind:方法，里面通过for循环直接完成了所有的操作，最后生成了RACEagerSequence对象。其实这个方法就是区分冷序列与热序列的关键。

这里一旦调用bind:方法，生成的序列的所有序列值就已经确定了。而对于冷信号调用bind:方法之后，并不会做一些数据有关的操作，只有获取head or tail 的时候才开始进行数据的处理操作，确定序列的值。

测试用例：

- (void)test_bind
{
    NSArray *array = @[@1, @3];
    RACArraySequence *arraySequence = [RACArraySequence sequenceWithArray:array offset:0];
    RACEagerSequence *eagerSequence = [RACEagerSequence sequenceWithArray:array offset:0];
    RACStreamBindBlock (^block)(void) = ^{
        return ^(id value, BOOL *stop) {
            return [RACSequence return:@"10000"];
        };
    };
    NSLog(@"bind -- %@ -- %@", [arraySequence bind:block], [eagerSequence bind:block]);

    // 打印日志：
    /*
     2018-08-17 17:57:46.320620+0800 TestRACEagerSequence[53678:18449077] bind -- <RACDynamicSequence: 0x600000099320>{ name = , head = (unresolved), tail = (unresolved) } -- <RACEagerSequence: 0x600000229740>{ name = , array = (
     10000,
     10000
     ) }
     */
}

---

- (instancetype)concat:(RACSequence *)sequence {
    NSCParameterAssert(sequence != nil);
    NSCParameterAssert([sequence isKindOfClass:RACSequence.class]);

    NSArray *array = [self.array arrayByAddingObjectsFromArray:sequence.array];
    return [[self.class sequenceWithArray:array offset:0] setNameWithFormat:@"[%@] -concat: %@", self.name, sequence];
}

重写concat:方法，直接进行数据的拼接操作。

测试用例：

- (void)test_concat
{
    RACEagerSequence *sequence1 = [RACEagerSequence sequenceWithArray:@[@1, @3] offset:0];
    RACEagerSequence *sequence2 = [RACEagerSequence sequenceWithArray:@[@2, @4] offset:1];
    NSLog(@"concat -- %@", [sequence1 concat:sequence2]);

    // 打印日志：
    /*
     2018-08-17 18:00:04.416837+0800 TestRACEagerSequence[53765:18456163] concat -- <RACEagerSequence: 0x600000229760>{ name = , array = (
     1,
     3,
     4
     ) }
     */
}

---

- (RACSequence *)eagerSequence {
    return self;
}

返回自身，自身就是一个热序列。

测试用例：

- (void)test_eagerSequence
{
    RACEagerSequence *sequence = [RACEagerSequence return:@(1)];
    NSLog(@"eagerSequence -- %@ -- %@", sequence, [sequence eagerSequence]);

    // 打印日志：
    /*
     2018-08-17 18:03:13.999872+0800 TestRACEagerSequence[53887:18465238] eagerSequence -- <RACEagerSequence: 0x604000230f60>{ name = , array = (
     1
     ) } -- <RACEagerSequence: 0x604000230f60>{ name = , array = (
     1
     ) }
     */
}

---

 - (RACSequence *)lazySequence {
    return [RACArraySequence sequenceWithArray:self.array offset:0];
}

返回RACArraySequence对象，即冷序列。

测试用例：

- (void)test_lazySequence
{
    RACEagerSequence *sequence = [RACEagerSequence sequenceWithArray:@[@1, @2] offset:0];
    NSLog(@"lazySequence -- %@ -- %@", sequence, [sequence lazySequence]);

    // 打印日志：
    /*
     2018-08-17 18:05:04.759838+0800 TestRACEagerSequence[53978:18470702] lazySequence -- <RACEagerSequence: 0x60400023cd40>{ name = , array = (
     1,
     2
     ) } -- <RACArraySequence: 0x60400023cd80>{ name = , array = (
     1,
     2
     ) }
     */
}

---

- (id)foldRightWithStart:(id)start reduce:(id (^)(id, RACSequence *rest))reduce {
    return [super foldRightWithStart:start reduce:^(id first, RACSequence *rest) {
        return reduce(first, rest.eagerSequence);
    }];
}

重写foldRightWithStart:reduce:方法，将从父类中获取的RACSequence对象调用eagerSequence方法转换成热序列，保证这个方法中所有涉及到的序列都是热序列。

测试用例：

- (void)test_foldRightWithStart
{
    RACArraySequence *sequence = [RACArraySequence sequenceWithArray:@[@1, @2, @3] offset:0];
    NSLog(@"foldRightWithStart -- %@", [sequence foldRightWithStart:@100 reduce:^id(id first, RACSequence *rest) {
        id result;
        for (id value in [rest array]) {
            result = @([value intValue] + [result intValue]);
        }
        return @([first intValue] + [result intValue]);
    }]);

    // 打印日志：
    /*
     2018-08-17 18:11:50.888905+0800 TestRACEagerSequence[54231:18490439] foldRightWithStart -- 106
     */
}

---

所以这个类就是一个热序列，通过bind:方法保证数据的操作立即执行。

到这里已经把RACSequence相关的类全部分析完了，上面的测试用例也全部可以在github上找到。