PHP RFC: Make constructors and destructors return void

• Date: 2020-06-17
• Author: Benas Seliuginas, benas.molis.iml@gmail.com
• Target version: PHP 8.0
• Status: Under Discussion

Large credit for this RFC goes to Michael Voříšek who initially reported the bug and created a draft-- patch.

At the moment, constructors and destructors can return values. However, these magic methods are supposed to be void (according to the documentation) and should not return a value. This RFC proposes to deprecate this behavior in PHP 8.0 and subsequently in PHP 9.0 enforce void rules on constructors and destructors.

This would apply both implicitly, where no return type is declared for the constructor/destructor, and explicitly where a void return type is declared.

Currently, void rules are not enforced for constructors and destructors. Thus, it is allowed to return values from those magic methods:

<?php
class Test {
	public function __construct() {
		return 0;
	}
 
	public function __destruct() {
		return 1;
	}
}
 
$test = new Test();
 
// this prints 0
echo $test->__construct();
// this prints 1
echo $test->__destruct();

But the PHP manual states, that constructors have void return type (i. e. don't return a value). Therefore, the current behavior is inconsistent and incorrect. The void return type rule should always be enforced on constructors/destructors, no matter if the void return type declaration is implicit or explicit.

This RFC proposes:

• to deprecate the ability of returning values from constructors and destructors in PHP 8.0.
• to treat both constructors and destructors that do not have an explicit return type, as if they have a return type of void in PHP 9.0.
• to allow explicit void return type on constructors and destructors.

A deprecation warning would be generated:

• for any constructor or destructor that returns a value in PHP 8.0.

A fatal error would be generated:

• for any constructor or destructor that returns a value in PHP 9.0.
• for any constructor or destructor that has an explicit return type other than void.

<?php
class Test {
	public function __construct() {
		// this is illegal
		return 0;
	}
 
	// this is illegal
	public function __destruct(): mixed {}
}
 
class Test2 {
	// this is legal
	public function __construct(): void {}
 
	// this is also legal
	public function __destruct() {}
}

Accepting this RFC results in a small backwards compatibility break in PHP 9.0 since it will no longer be legal to return (mixed and any of its subtypes) values from constructors and destructors.

The position of this RFC is that this BC break is minimal, as returning values from constructors/destructors is not a standard pattern used by many pieces of code. However, to minimize the number of BC breaks even further, the ability of returning values from constructors/destructors is deprecated in PHP 8.0.

Explicitly declaring the return type declaration would be optional. It would still be allowed to not specify a type at all:

<?php
class Test {
	// this is legal
	public function __construct() {}
 
	// this is also legal
	public function __destruct(): void {}
}

Since constructors are exempt from inheritance checks, it is allowed to widen the type from a child class. For example, if the parent class has explicitly declared the constructor as void, it would still be allowed to widen the type to no return type. In other words, covariance (for return types) does not apply to constructors.

<?php
class Test {
	// this is legal
	public function __construct(): void {}
}
 
class Test2 extends Test {
	// this is also legal
	public function __construct() {}
}

Should we enforce void rules on constructors and destructors in PHP 8.1 or PHP 9.0?

2/3 majority Yes/No.

GitHub Pull Request