相关疑难解决方法(0)

Either类似乎很有用,使用它的方法非常明显.但后来我看了API文档,我很困惑:

def joinLeft [A1 >: A, B1 >: B, C] (implicit ev: <:<[A1, Either[C, B1]]):
         Either[C, B1]
   Joins an Either through Left.

def joinRight [A1 >: A, B1 >: B, C] (implicit ev: <:<[B1, Either[A1, C]]):
         Either[A1, C]
   Joins an Either through Right.

def left : LeftProjection[A, B]
   Projects this Either as a Left.

def right : RightProjection[A, B]
   Projects this Either as a Right.

我如何处理投影,如何调用连接？

Google只是向我指出了API文档.

这可能只是"不关注幕后人"的情况,但我不这么认为.我认为这很重要.