scala – 匹配可能不是详尽的警告是不正确的

abstract class Foo {
    def foo(that: Foo): Unit = (this,that) match {
        case (Foo_1(),Foo_1()) => //case 1
        case (Foo_1(),Foo_2()) => //case 2
        case (Foo_2(),Foo_1()) => //case 3
        case (Foo_2(),Foo_2()) => //case 4
            // Compiler warning
    }

    def fooThis(): Unit = this match {
        case Foo_1() => //do something
        case Foo_2() => //do something
            // Works fine
    }

    def fooThat(that: Foo): Unit = that match {
        case Foo_1() => //do something
        case Foo_2() => //do something
            // Works fine
    }
}
case class Foo_1() extends Foo
case class Foo_2() extends Foo

这是错误：

Warning:(5,32) match may not be exhaustive.
It would fail on the following inputs: (Foo(),_),(Foo_1(),(Foo_2(),(_,Foo()),Foo_1()),Foo_2()),_)
    def foo(that: Foo): Unit = (this,that) match {

由于这个和Foo类型,并且Foo只能是Foo_1或Foo_2类型,因此foo中的情况都是可能的组合.

为了完整起见,我添加了fooThis和fooThat,并表明匹配Foo_1和Foo_2就足够了.编译器消息表明还有其他类型可以匹配(即Foo和_).

那么为什么会出现这个警告呢？

有关：

> Scala bug: fixed in 2.12.0-M4.我的scala欢迎辞：

Welcome to Scala 2.12.1 (Java HotSpot(TM) Client VM,Java 1.8.0_131).

> Scala bug: false match not exhaustive warning on (unsealed,sealed) tuple

编辑

一旦你使用元组,编译器似乎就会抱怨.如果我们将一个虚拟变量添加到fooThis,如下所示

def fooThis(): Unit = (this,Foo_1()) match {
    case (Foo_1(),_) => //do something
    case (Foo_2(),_) => //do something
}

我们得到以下编译器警告

Warning:(13,27) match may not be exhaustive.
It would fail on the following input: (_,_)
    def fooThis(): Unit = (this,Foo_1()) match {