Add a cross-crate test for casting classes to ifaces

src/test/run-pass/class-cast-to-iface-cross-crate.rs

+import to_str::*;
+import to_str::to_str;
+
+class cat implements to_str {
+  priv {
+    let mut meows : uint;
+    fn meow() {
+      #error("Meow");
+      self.meows += 1u;
+      if self.meows % 5u == 0u {
+          self.how_hungry += 1;
+      }
+    }
+  }
+
+  let mut how_hungry : int;
+  let name : str;
+
+  new(in_x : uint, in_y : int, in_name: str)
+    { self.meows = in_x; self.how_hungry = in_y; self.name = in_name; }
+
+  fn speak() { self.meow(); }
+
+  fn eat() -> bool {
+    if self.how_hungry > 0 {
+        #error("OM NOM NOM");
+        self.how_hungry -= 2;
+        ret true;
+    }
+    else {
+        #error("Not hungry!");
+        ret false;
+    }
+  }
+
+  fn to_str() -> str { self.name }
+}
+
+fn print_out<T: to_str>(thing: T, expected: str) {
+  let actual = thing.to_str();
+  #debug("%s", actual);
+  assert(actual == expected);
+}
+
+fn main() {
+  let nyan : to_str  = cat(0u, 2, "nyan") as to_str;
+  print_out(nyan, "nyan");
+}
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