Online PHP editor | rfc for qMZOH

@ 2025-03-31T20:58:37Z

<?php

interface I {
  public function a(int $a): string;
}

Class C implements I {
  public function a(int|string $a): string {
    return "foo";
  }
}

class D implements I {
    public function a(int $a): string {
        return "foo";
    }
}

/**
 * `test` from previous example (https://3v4l.org/5YPdg) does not respect I.
 * It calls with a string instead of an int (which is what I requires), thus the $subject->a()
 * call will fail at runtime for any implementation of I that doesn't widen the type.
 */
function ignores_i(I $subject) {
    print $subject->a("beep");
}

/**
 * This implementation respects the interface--the $subject->a() call will
 * _never_ result in a type error at runtime
 */
function respects_i(I $subject) {
    print $subject->a(123);
}

/**
 * Widening int => int|string _is_ useful, becacuse we can also write code against
 * this concrete type, and here we _can_ safely pass a string.
 */
function uses_concrete_type(C $subject)
{
    $subject->a("beep");
}

respects_i(new C()); // works
respects_i(new D()); // works
uses_concrete_type(new C()); // works
ignores_i(new C()); // works
ignores_i(new D()); // type error

Output for git.master_jit, git.master: foofoofoo Fatal error: Uncaught TypeError: D::a(): Argument #1 ($a) must be of type int, string given, called in /in/qMZOH on line 25 and defined in /in/qMZOH:14 Stack trace: #0 /in/qMZOH(25): D->a('beep') #1 /in/qMZOH(49): ignores_i(Object(D)) #2 {main} thrown in /in/qMZOH on line 14
Process exited with code 255.

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2020-03-21 RFC: Is_Literal - declined
2020-12-04 Enumerations - included in PHP 8.1
2018-06-15 Typed Properties v2 - implemented in PHP 7.4
2016-08-12 Object typehint - included in PHP 7.2
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