hphp/hack/test/typecheck/contravariance_unresolved_bad_2.php

   1 <?hh // strict
   2 // Copyright 2004-present Facebook. All Rights Reserved.
   3
   4 interface I1<-T> {
   5   public function f(T $t): int;
   6 }
   7
   8 final class C1 implements I1<string> {
   9   public function f(string $t): int {
  10     return 42;
  11   }
  12 }
  13
  14 final class C2<T> {
  15   public function __construct(private I1<T> $impl) {}
  16   public function f(T $t): int {
  17     return $this->impl->f($t);
  18   }
  19 }
  20
  21 class Foo {
  22   public function BreakIt(): void {
  23     $c1 = new C1();
  24
  25     // the following line is caught by type checker
  26     // $c1->f(42);
  27
  28     $c2 = new C2($c1);
  29     // What type do we expect for $c2?
  30     // Perhaps C2<string>?
  31     // What actually happens is
  32     // $c2 : C2<v:=unresolved{}>
  33     // and then check C1 <: I1<v:=unresolved{}>
  34     // and so I1<string> <: I1<v:=unresolved{}>
  35     // and so v:=unresolved{} <: string
  36
  37     // the following line fails in runtime
  38     $c2->f(42);
  39   }
  40 }
  41
  42 function main(): void {
  43   (new Foo())->BreakIt();
  44 }