From 0e306e1f90f51efa2d423fd7df810f7cc8dfa915 Mon Sep 17 00:00:00 2001
From: Paul Phillips <paulp@improving.org>
Date: Sun, 19 Dec 2010 23:20:13 +0000
Subject: Explaining something for the (largeish N)th tim...

Explaining something for the (largeish N)th time finally awoke me to
the fact that software can explain things. I labored a long time over
this error message: I'm sure it can still use work (and/or it will drive
scalaz users off some kind of cliff) but the simple common case people
have so much trouble with is lit up like a christmas tree and for this I
will take some bullets.

  build/pack/bin/scala -e 'class Foo[T] ; Set[Foo[AnyRef]]() + new
  Foo[String]' :1: error: type mismatch; found : this.Foo[String]
  required: this.Foo[java.lang.Object] Note: String <: java.lang.Object,
  but class Foo is invariant in type T. You may wish to define T as +T
  instead. (SLS 4.5) class Foo[T] ; Set[Foo[AnyRef]]() + new Foo[String]
  ^

Review by moors.
---
 test/files/neg/found-req-variance.scala | 106 ++++++++++++++++++++++++++++++++
 1 file changed, 106 insertions(+)
 create mode 100644 test/files/neg/found-req-variance.scala

(limited to 'test/files/neg/found-req-variance.scala')

diff --git a/test/files/neg/found-req-variance.scala b/test/files/neg/found-req-variance.scala
new file mode 100644
index 0000000000..c44d021fac
--- /dev/null
+++ b/test/files/neg/found-req-variance.scala
@@ -0,0 +1,106 @@
+import scala.collection.mutable.ListBuffer
+
+class A
+class B extends A
+class C extends B
+
+trait FF1[T, +R]
+trait FF2[-T, R]
+
+class Inv[T]
+class InvA extends Inv[A]
+class InvB extends Inv[B]
+class InvC extends Inv[C]
+
+class Multi[+Cov, Inv, -Con]
+class MultiCov[+T <: A] extends Multi[T, B, C]
+class MultiInv[T] extends Multi[A, T, C]
+class MultiCon[-T >: C] extends Multi[A, B, T]
+
+object Test {
+  def f1 = Set[Inv[A]]() + new Inv[A]
+  def f2 = Set[Inv[A]]() + new Inv[B]
+  def f3 = Set[Inv[A]]() + new Inv[C]
+  def f4 = Set[Inv[B]]() + new Inv[A]
+  def f5 = Set[Inv[B]]() + new Inv[B]
+  def f6 = Set[Inv[B]]() + new Inv[C]
+  def f7 = Set[Inv[C]]() + new Inv[A]
+  def f8 = Set[Inv[C]]() + new Inv[B]
+  def f9 = Set[Inv[C]]() + new Inv[C]
+
+  def g1 = Set[Multi[A, B, C]]() + new MultiCov[A]
+  def g2 = Set[Multi[A, B, C]]() + new MultiCov[B]
+  def g3 = Set[Multi[A, B, C]]() + new MultiCov[C]
+  def g4 = Set[Multi[A, B, C]]() + new MultiInv[A]
+  def g5 = Set[Multi[A, B, C]]() + new MultiInv[B]
+  def g6 = Set[Multi[A, B, C]]() + new MultiInv[C]
+  def g7 = Set[Multi[A, B, C]]() + new MultiCon[A]
+  def g8 = Set[Multi[A, B, C]]() + new MultiCon[B]
+  def g9 = Set[Multi[A, B, C]]() + new MultiCon[C]
+}
+
+object Functions {
+  object Set1 {
+    def f[T, R](x: FF1[T, R]) = ()
+    def h[T, R] : FF1[T, R] = system.error("")
+
+    def ff1 = f[B, B](h[A, A]) // fail
+    def ff2 = f[B, B](h[B, A]) // fail
+    def ff3 = f[B, B](h[C, A]) // fail
+    def ff4 = f[B, B](h[A, B]) // suggest
+    def ff5 = f[B, B](h[B, B]) // ok
+    def ff6 = f[B, B](h[C, B]) // suggest
+    def ff7 = f[B, B](h[A, C]) // suggest
+    def ff8 = f[B, B](h[B, C]) // ok
+    def ff9 = f[B, B](h[C, C]) // suggest
+  }
+  object Set2 {
+    def f[T, R](x: FF2[T, R]) = ()
+    def h[T, R] : FF2[T, R] = system.error("")
+
+    def ff1 = f[B, B](h[A, A]) // suggest
+    def ff2 = f[B, B](h[B, A]) // suggest
+    def ff3 = f[B, B](h[C, A]) // fail
+    def ff4 = f[B, B](h[A, B]) // ok
+    def ff5 = f[B, B](h[B, B]) // ok
+    def ff6 = f[B, B](h[C, B]) // fail
+    def ff7 = f[B, B](h[A, C]) // suggest
+    def ff8 = f[B, B](h[B, C]) // suggest
+    def ff9 = f[B, B](h[C, C]) // fail
+  }
+}
+
+// TODO
+// object TypeAlias {
+//   type LL[T] = List[T]
+//   val LL = List
+//
+//   def f1 = Set[LL[B]]() + LL[A](new A)
+//   def f2 = Set[LL[B]]() + LL[C](new C)
+// }
+
+object Javas {
+  def f[T](x: java.util.List[T]) = ()
+  def g[T](x: java.util.Comparator[T]) = ()
+
+  def g1 = f[AnyRef](new java.util.ArrayList[String] { })
+  def g2 = g[String](Ordering.fromLessThan[AnyRef](_.toString < _.toString))
+}
+
+object Misc {
+  // original motivation
+  class Data[A <: AnyVal]
+  class MyData extends Data[Int] { }
+  def f1 = Set[Data[AnyVal]]() + new MyData
+
+  // from stackoverflow
+  def foo(s: Set[CharSequence]): Unit = ()
+  def f4 = {
+    val s: Set[String] = Set("Hello", "World");
+    foo(s)
+  }
+
+  class Trippy[+T1, T2, +T3]
+  def g1 = Set[Trippy[AnyRef, AnyRef, AnyRef]]() + new Trippy[String, String, String]
+  def g2 = Set[Map[String, String]]() + Map[AnyRef, String]()
+}
\ No newline at end of file
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