CODEWITHSUNDEEP
scala
Kevin Meredith
Kevin Meredith

Reputation: 41909

Path-dependent Types and Type Projection

As I understand the def bar(x: X#Inner) signature, it simply requires any instance of Inner to compile successfully. Whereas, foo(x: this.Inner) will only compile with the same Outer.Inner class instance.

While reading Scala in Depth, I put this code into REPL, but I'm getting a compile-time error.

scala> class Outer {
     |    trait Inner
     |     def y = new Inner {}
     |    def foo(x: this.Inner) = null
     |    def bar(x: X#Inner) = null
     | }
<console>:11: error: not found: type X
          def bar(x: X#Inner) = null
                     ^

Also, what is the compile-time error here?

Upvotes: 0

Views: 152

Answers (2)

0__
0__

Reputation: 67280

The X in X#Inner refers to the outer type. You do not have a type X anywhere, that's what the compiler error says exactly.

In your example you will want to refer to type Outer instead:

class Outer {
  trait Inner
  def foo(x: this.Inner) = ???
  def bar(x: Outer#Inner) = ???
}

Upvotes: 1

dadanier
dadanier

Reputation: 161

X#Inner should be Outer#Inner，I think the author of Scala in depth just typed falsely in the book.

Upvotes: 0

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