hphp/hack/test/typecheck/meth_caller6.php

   1 <?hh // strict
   2 /**
   3  * Copyright (c) 2014, Facebook, Inc.
   4  * All rights reserved.
   5  *
   6  * This source code is licensed under the MIT license found in the
   7  * LICENSE file in the "hack" directory of this source tree.
   8  *
   9  *
  10  */
  11
  12 abstract class E {
  13   public function foo(): void {}
  14 }
  15
  16 final class A<T as E> {
  17
  18   public function __construct((function(T): void) $x) {}
  19
  20 }
  21
  22 function test1<T as E>(): A<T> {
  23   return new A(meth_caller('E', 'foo'));
  24 }
  25
  26 function test2<T as E>(): A<T> {
  27   // Type of $f should be
  28   //   function(E):void
  29   $f = meth_caller(E::class, 'foo');
  30   // Now type of $r should be
  31   //   A<x>
  32   // with constraint that
  33   //   x <: E
  34   //   function(E):void <: function(x):void
  35   // i.e.
  36   //   x <: E (contravariance), so we're ok
  37   $r = new A($f);
  38   // Now we need to check the return type
  39   //   A<x> <: A<T>
  40   // So by invariance we have x=T, and we're ok
  41   // because of the T as E constraint
  42   return $r;
  43 }