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Bug #81306 PHP doesn't fully evaluate new expressions passed in named arguments
Submitted: 2021-07-28 20:35 UTC Modified: 2021-07-28 21:36 UTC
From: raincomplain at outlook dot com Assigned:
Status: Not a bug Package: Scripting Engine problem
PHP Version: 8.1.0beta1 OS:
Private report: No CVE-ID: None
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 [2021-07-28 20:35 UTC] raincomplain at outlook dot com 
Description:
------------
According to the RFC of "New in initializers":

Parameter default values are evaluated from left to right on every call to the function where the parameter is not explicitly passed.

So calling a method by not explicitly passing a default paramater and using named arguments to call other arguments should trigger default parameter evaluation, so far so good. However, if both arguments are objects of the same class that modify a static property, PHP only returns the copy of the default object and "overlooks" the other object that was passed as a named argument.

Test script:
---------------
class A
{
    public static int $x = 0;

    public function __construct(int $x)
    {
        self::$x = $x; // changing this to self::$x += $x; works as expected
    }
}

function getTest(A $o1 = new A(88), A $o2 = new A(77))
{
    return A::$x;
}

var_dump(getTest(o2: new A(55)))

Expected result:
----------------
int(55)

Actual result:
--------------
int(88)

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 [2021-07-28 20:44 UTC] nikic@php.net
-Status: Open +Status: Not a bug
 [2021-07-28 20:44 UTC] nikic@php.net 
This example is extremely weird. Let's make it more obvious by dropping the static property and just dumping in the constructor:

<?php

class A {
    public function __construct(int $x) {
        var_dump($x);
    }
}

function getTest(A $o1 = new A(88), A $o2 = new A(77)) {
}

getTest(o2: new A(55));

This prints int(55) followed by int(88), exactly as it should. First the new A(55) object is created explicitly and passed to parameter $o2, and then new A(88) is created when filling in the default value for parameter $o1.
 [2021-07-28 21:00 UTC] raincomplain at outlook dot com 
We can't dropp the static property because then there will be no bug. 
Isn't: 
var_dump(getTest(new A(88),  new A(55))) 

equivalant to: 
var_dump(getTest(o2: new A(55)))

in my test script ?
 [2021-07-28 21:14 UTC] raincomplain at outlook dot com 
If they are equivalant(as I believe)then this is a bug.
 [2021-07-28 21:27 UTC] nikic@php.net 
They are only the same modulo evaluation order, and evaluation order is relevant in this example. The explicitly passed arguments are evaluated before any parameter default values.
 [2021-07-28 21:36 UTC] raincomplain at outlook dot com 
Thanks Nikita, I was wrong when I thought parameter default values are evalutaed first.
 
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