The "new" operator should emit TypeErrors on __construct() return values.

[MircoBabin]

Description

The "new" operator and __construct() return values

• To my surprise return $this; in the __construct() function gives the error Using $this when not in object context. If this is the corrrect errortext is debatable, but this is correct behavior, it is not allowed.
• But returning anything but $this does not fail. Which is very strange. This is only in combination with the "new" operator. The "new" operator should emit TypeError for all return values.
• When calling __construct() as a regular function a return value might have some purpose. But why not deprecate calling __construct() outside the new operator?

P.S. If it should be a TypeError or some other error is debatable. But at least it should error.

Reproduce

The following code:

https://3v4l.org/sXXe8#v8.5.2

<?php

const SOMECONST = 'Const hello';

enum SomeEnum 
{
    case Hearts;
    case Diamonds;
    case Clubs;
    case Spades;
}

function SomeFunction()
{
}

$SomeFunctionClosure = function()
{
};

$SomeFunctionFirstClassCallable = SomeFunction(...);

$someFunctionClosureFromCallabe = Closure::fromCallable('SomeFunction');

class ShouldTypeError
{
    public function __construct($returnValue)
    {
        if ($returnValue !== 'no-return') {
            if ($returnValue === '$this') {
                return $this;
            } elseif ($returnValue === 'no-return-value') {
                return;
            } elseif ($returnValue === 'void') {
                return void;
            } elseif ($returnValue === 'never') {
                return never;
            }
            
            return $returnValue;
        }
    }
}

$testcases = [
    'no-return',
    'no-return-value',
    '$this',
    new ShouldTypeError('no-return'),

    SOMECONST,    
    'abc',
    1,
    1.23,
    null,
    true,
    false,
    
    ['a', 'b', 'c'],
    ['a' => 'a', 'b' => 'b', 'c' => 'c', 0 => 'Zero'],
    
    'never',
    'void',
    
    SomeEnum::Spades,
    
    function() {
       echo 'Hi'.PHP_EOL;
    },
    $SomeFunctionClosure,
    $SomeFunctionFirstClassCallable,
    $someFunctionClosureFromCallabe,
    
    new DateTimeImmutable(),
];

foreach($testcases as $testcase) {
    echo "--------------[ TESTCASE ]--------------\n";
    var_dump($testcase);
    echo "\n";
    
    try {
        $didReturn = new ShouldTypeError($testcase);
        
        switch($testcase) {
            case 'no-return':
                echo "Success: without a return statement is always valid.\n";
                break;

            case 'no-return-value':
                echo "Success: a return statement without a value is always valid.\n";
                break;

            case '$this':
                echo "Dubious: return $this is dubious.\n";
                echo "- it fullfills the return type, so it could be allowed.\n";
                echo "- but returning anything from a constructor is nonsense, because it is discarded.\n";
                echo "  As shown by the third testcase new SomeTypeError('no-return').\n";
                break;
                
            default:
                echo "Error: why is it not a return TypeError?\n";
                break;
        }
        
        if (!($didReturn instanceof ShouldTypeError)) {
            echo "Failed to new a ShouldTypeError.\n";
        }
    } catch (Throwable $ex) {
        echo "Success: throwable: ".$ex->getMessage()."\n";
    }
}

Resulted in this output (php 8.5.2):

--------------[ TESTCASE ]--------------
string(9) "no-return"

Success: without a return statement is always valid.
--------------[ TESTCASE ]--------------
string(15) "no-return-value"

Success: a return statement without a value is always valid.
--------------[ TESTCASE ]--------------
string(5) "$this"

Success: throwable: Using $this when not in object context
--------------[ TESTCASE ]--------------
object(ShouldTypeError)#4 (0) {
}

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
string(11) "Const hello"

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
string(3) "abc"

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
int(1)

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
float(1.23)

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
NULL

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
bool(true)

Success: without a return statement is always valid.
--------------[ TESTCASE ]--------------
bool(false)

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
array(3) {
  [0]=>
  string(1) "a"
  [1]=>
  string(1) "b"
  [2]=>
  string(1) "c"
}

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
array(4) {
  ["a"]=>
  string(1) "a"
  ["b"]=>
  string(1) "b"
  ["c"]=>
  string(1) "c"
  [0]=>
  string(4) "Zero"
}

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
string(5) "never"

Success: throwable: Undefined constant "never"
--------------[ TESTCASE ]--------------
string(4) "void"

Success: throwable: Undefined constant "void"
--------------[ TESTCASE ]--------------
enum(SomeEnum::Spades)

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
object(Closure)#6 (3) {
  ["name"]=>
  string(22) "{closure:/in/sXXe8:67}"
  ["file"]=>
  string(9) "/in/sXXe8"
  ["line"]=>
  int(67)
}

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
object(Closure)#1 (3) {
  ["name"]=>
  string(22) "{closure:/in/sXXe8:17}"
  ["file"]=>
  string(9) "/in/sXXe8"
  ["line"]=>
  int(17)
}

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
object(Closure)#2 (1) {
  ["function"]=>
  string(12) "SomeFunction"
}

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
object(Closure)#3 (1) {
  ["function"]=>
  string(12) "SomeFunction"
}

Error: why is it not a return TypeError?
--------------[ TESTCASE ]--------------
object(DateTimeImmutable)#7 (3) {
  ["date"]=>
  string(26) "2026-01-30 13:31:14.025598"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(16) "Europe/Amsterdam"
}

Error: why is it not a return TypeError?

PHP Version

PHP 8.5.2 via 3v4l

Operating System

3v4l

[MircoBabin]

I forgot to add a resource test. I expanded the $testcases[] array with fopen('php://memory', 'w+'),.

See https://3v4l.org/kP3ZJ#v8.5.2

[iluuu1994]

Hi @MircoBabin.

To my surprise return $this; in the __construct() function gives the error Using $this when not in object context. If this is the corrrect errortext is debatable, but this is correct behavior, it is not allowed.

The error comes from this line:

echo "Dubious: return $this is dubious.\n";

Where $this is interpolated, and accessed outside of a class context.

When calling __construct() as a regular function a return value might have some purpose. But why not deprecate calling __construct() outside the new operator?

This is a frequent use-case for (un)serializers.