Merge pull request #5207 from dotty-staging/fix-intersection-docs

Clarifications in the docs on intersection types

Author: odersky

docs/docs/reference/intersection-types.md

@@ -20,16 +20,16 @@ def f(x: Resettable & Growable[String]) = {
 
 The value `x` is required to be _both_ a `Resettable` and a
 `Growable[String]`.  Intersection types `A & B` replace compound types
-`A with B` in Scala 2 (for the moment, `A with B` is still allowed, but
-it will be deprecated and removed in the future).
-
-Unlike `with` types, `&` is _commutative_: `A & B` is the same type as
-`B & A`.
+`A with B` in Scala 2. For the moment, `A with B` is still allowed, but
+its usage as a type (as opposed to in a `new` or `extends` clause) will be deprecated and removed in the future.
 
 The members of an intersection type `A & B` are all the members of `A`
 and all the members of `B`. For instance `Resettable & Growable[String]`
 has member methods `reset` and `add`.
 
+`&` is _commutative_: `A & B` is the same type as `B & A`, in that sense that the two types
+have the same values and are subtypes of each other.
+
 If a member appears in both `A` and `B`, its type in `A & B` is the
 intersection of its type in `A` and its type in `B`. For instance, assume the definitions:
 

tests/pos/intersection.scala

@@ -22,3 +22,22 @@ object intersection {
   def g: C[A | B] = f
   def h: C[A] & C[B] = g
 }
+object Test {
+
+  trait A {
+    def f: Any
+  }
+  trait B extends A {
+    override def f: Int = 1
+  }
+  trait C extends A {
+    def f: Any = ""
+  }
+
+  val bc: B with C = new C with B {}
+
+  def fooAB = (??? : A with B).f
+  def fooAB1: Int = fooAB
+  def fooBA = (??? : B with A).f
+  def fooBA1: Int = fooBA
+}