Table of Contents

PHP RFC: Deprecate returning values from __construct() and __destruct()

Introduction

A class’ constructor and destructor (“Lifecycle Functions”) are special in that they are not meant to be used like regular methods and called manually. Observing the return value during intended use is not possible.

To that effect they are already restricted from declaring any return type at all, including declaring a return type of void. It however is nevertheless legal to return a value from these methods, which can be confusing, particularly when returning a separate valid object instance from __construct().

Proposal

Deprecate returning values from __construct() and __destruct(). Using return …; shall emit a compile-time deprecation. Using return; without an expression to “skip” over the remaining logic shall remain legal. Since Generators effectively return a new Generator object, making __construct() and __destruct() a Generator shall also be deprecated. Starting with the next major version, returning a value shall emit a compile-time error. 

<?php
 
class Foo
{
	public function __construct()
	{
		return 123; // Deprecated: Returning a value from a constructor is deprecated in test.php on line 6
	}
 
	public function __destruct()
	{
		return 123; // Deprecated: Returning a value from a constructor is deprecated in test.php on line 12
	}
}
 
class Bar
{
	public function __construct()
	{
		if (random_int(0, 1)) {
			return; // Skipping the rest of the logic remains legal.
		}
 
		echo "Constructing", PHP_EOL;
	}
}
 
class Baz
{
	public function __construct()
	{
		yield 123; // Deprecated: Making a constructor a Generator is deprecated in test.php on line 30
	}
 
	public function __destruct()
	{
		yield 123; // Deprecated: Making a destructor a Generator is deprecated in test.php on line 35
	}
}

This deprecation is in line with the existing error when returning a value from a void function: 

<?php
 
function void_function(): void
{
	return 123; // Fatal error: A void function must not return a value in test.php on line 5
}

It will remain legal to manually call __construct() and __destruct(), for example to call a parent constructor or destructor - or to initialize a lazy object.

Backward Incompatible Changes

The deprecation itself is not a backwards incompatible change. When it is turned into an error, code that returns values will stop working. The justification is provided in the introduction.

Proposed PHP Version(s)

Deprecation in the next PHP version (8.6). Removal in the first major after that.

RFC Impact

To the Ecosystem

Static analyzers and IDEs will want to point out:

An analysis of the top 4000 composer packages run by Juliette Reinders Folmer with PHP_CodeSniffer revealed a total of 77 return statements with a value across 59 files and 36 packages. 2 of the return statements were inside __destruct(). 21 were of the form return $this;. One returned the value of a static property containing a non-$this object.

This indicates that albeit rare, there appears to be some misunderstanding of how constructors and destructors work in PHP that can be cleared up by deprecating this behavior.

To Existing Extensions

None.

To SAPIs

None.

Open Issues

None.

Future Scope

Similar arguments apply to __clone(). However in that case specifying an explicit return type of void is legal. __clone() will therefore implicitly be handled if / when magic methods are required to specify accurate return (and parameter) types.

Voting Choices

Primary Vote requiring a 2/3 majority to accept the RFC:

Deprecate returning values from __construct() and __destruct()?
Real name Yes No Abstain
Final result: 0 0 0
This poll has been closed.

Patches and Tests

https://github.com/php/php-src/pull/21982

Implementation

After the RFC is implemented, this section should contain:

  1. the version(s) it was merged into
  2. a link to the git commit(s)
  3. a link to the PHP manual entry for the feature

References

Rejected Features

None.

Changelog