hphp/hack/test/typecheck/xor_params.php

   1 <?hh // strict
   2 // Copyright 2004-present Facebook. All Rights Reserved.
   3
   4 function nullthrows<T>(?T $x): T {
   5   return $x as nonnull;
   6 }
   7
   8 final class XorParam<Tx, Ty> {
   9   private function __construct(private ?Tx $x, private ?Ty $y) {
  10     invariant(
  11       ($x === null) !== ($y === null),
  12       "Exactly one input value must be null!",
  13     );
  14   }
  15
  16   public static function fromFirstValue(?Tx $x, ?Ty $y): XorParam<Tx, Ty> {
  17     if ($x !== null) {
  18       return new XorParam($x, null);
  19     }
  20     return new XorParam(null, $y);
  21   }
  22
  23   public function getX(): ?Tx {
  24     return $this->x;
  25   }
  26
  27   public function atX(): Tx {
  28     return nullthrows($this->x);
  29   }
  30
  31   public function getY(): ?Ty {
  32     return $this->y;
  33   }
  34
  35   public function atY(): Ty {
  36     return nullthrows($this->y);
  37   }
  38
  39   // Returns the single non-null value
  40   // TODO: is it possible to augment the type info within the generics so we
  41   // can type this return value?
  42   public function getValue(): mixed {
  43     $z = $this->x ?? $this->y;
  44     $w = nullthrows($z);
  45     return $w;
  46   }
  47 }