RACSequence分析（九）—— RACTupleSequence

RACTupleSequence作为RACSequence的子类，顾名思义，就是对元祖的操作，根据新增加的方法sequenceWithTupleBackingArray:offset:可知，该类是对元祖的数组对象做处理。

完整测试用例在这里。

.m中的方法如下：

+ (instancetype)sequenceWithTupleBackingArray:(NSArray *)backingArray offset:(NSUInteger)offset {
    NSCParameterAssert(offset <= backingArray.count);

    if (offset == backingArray.count) return self.empty;

    RACTupleSequence *seq = [[self alloc] init];
    seq->_tupleBackingArray = backingArray;
    seq->_offset = offset;
    return seq;
}

创建RACTupleSequence对象，保存参数值backingArray offset。

测试用例：

- (void)test_sequenceWithTupleBackingArray
{
    RACTuple *tuple = RACTuplePack(@1, @2, @3);
    RACSequence *sequence = [RACTupleSequence sequenceWithTupleBackingArray:tuple.allObjects offset:1];
    NSLog(@"sequenceWithTupleBackingArray -- %@", sequence);

    // 打印日志；
    /*
     2018-08-17 17:40:07.673830+0800 TestRACTupleSequence[52426:18393668] sequenceWithTupleBackingArray -- <RACTupleSequence: 0x600000236600>{ name = , tuple = (
     1,
     2,
     3
     ) }
     */
}

---

- (id)head {
    id object = self.tupleBackingArray[self.offset];
    return (object == RACTupleNil.tupleNil ? NSNull.null : object);
}

获取tupleBackingArray指定偏移量offset下的值作为head值。

测试用例：

- (void)test_head
{
    RACTuple *tuple = RACTuplePack(@1, @2, @3);
    RACSequence *sequence = [RACTupleSequence sequenceWithTupleBackingArray:tuple.allObjects offset:1];
    NSLog(@"head -- %@", sequence.head);

    // 打印日志；
    /*
     2018-08-17 17:41:34.131249+0800 TestRACTupleSequence[52496:18398390] head -- 2
     */
}

---

- (RACSequence *)tail {
    RACSequence *sequence = [self.class sequenceWithTupleBackingArray:self.tupleBackingArray offset:self.offset + 1];
    sequence.name = self.name;
    return sequence;
}

通过sequenceWithTupleBackingArray:offset:并将偏移量增加1生成一个RACSequence对象作为tail值。

测试用例：

- (void)test_tail
{
    RACTuple *tuple = RACTuplePack(@1, @2, @3);
    RACSequence *sequence = [RACTupleSequence sequenceWithTupleBackingArray:tuple.allObjects offset:1];
    NSLog(@"tail -- %@", sequence.tail);

    // 打印日志；
    /*
     2018-08-17 17:42:32.102848+0800 TestRACTupleSequence[52540:18401646] tail -- <RACTupleSequence: 0x60000022c300>{ name = , tuple = (
     1,
     2,
     3
     ) }
     */
}

---

- (NSArray *)array {
    NSRange range = NSMakeRange(self.offset, self.tupleBackingArray.count - self.offset);
    NSMutableArray *array = [[NSMutableArray alloc] initWithCapacity:range.length];

    [self.tupleBackingArray enumerateObjectsAtIndexes:[NSIndexSet indexSetWithIndexesInRange:range] options:0 usingBlock:^(id object, NSUInteger index, BOOL *stop) {
        id mappedObject = (object == RACTupleNil.tupleNil ? NSNull.null : object);
        [array addObject:mappedObject];
    }];

    return array;
}

通过tupleBackingArray调用enumerateObjectsAtIndexes:方法获取数组从指定偏移量offset开始的所有数据，组成一个新的数组返回。

测试用例：

- (void)test_array
{
    RACTuple *tuple = RACTuplePack(@1, @2, @3);
    RACSequence *sequence = [RACTupleSequence sequenceWithTupleBackingArray:tuple.allObjects offset:1];
    NSLog(@"array -- %@", sequence.array);

    // 打印日志；
    /*
     2018-08-17 17:43:20.283402+0800 TestRACTupleSequence[52589:18404640] array -- (
     2,
     3
     )
     */
}

---

所以该类的作用就是将元祖的数组转换成一个序列，通过序列的方法获取元祖的值。其实跟RACArraySequence的方法非常相似，只是RACArraySequence获取的值并不会做处理。而RACTupleSequence会将RACTupleNil类型转换为NSNull类型，如果对RACTuple有所了解，就会知道RACTuple某种情况下会将NSNull转为RACTupleNil，这里的操作刚好是还原原始数据。

如果对RACTuple不了解，请看这里。