PHP RFC: Nullable Return Types

• Version: 0.9
• Date: 2016-04-06
• Author: Dmitry Stogov, dmitry@zend.com
• Status: Under Discussion
• First Published at: https://wiki.php.net/rfc/nullable_return_types

PHP 7 introduced optional declaration of function return types.

function foo(): int {
}

However, it didn't make possible to mix declared return type with NULL. This leaded to inability to use return type declarations in many cases, like in the following example of binary-tree where the left and right nodes may be NULL by design.

class Node {
  private $left;
  private $right;

  function __construct(Node $left = null, Node $right = null) {
    $this->left = $left;
    $this->right = $right;
  }
  function getLeft() /* : Node */ {
    return $this->left;
  }
  function getRight() /* : Node */ {
    return $this->right;
  }
}

I propose to use HHVM compatible syntax to declare nullable return types - ?<type>

So the previous example will look like the following:

class Node {
  private $left;
  private $right;

  function __construct(Node $left = null, Node $right = null) {
    $this->left = $left;
    $this->right = $right;
  }
  function getLeft(): ?Node {
    return $this->left;
  }
  function getRight(): ?Node {
    return $this->right;
  }
}

Usage of the same ?<type> syntax for arguments (and later properties) is not the subject of this RFC. Actually, arguments already may be declared as “nullable” using NULL default value (the same may be done for properties). This decision(s) may be done separately.

NONE

This RFC targets PHP version 7.1.

NONE

This RFC doesn't propose any change to argument (or property) type declarations. The following code won't work, but this RFC doesn't prohibit to support this syntax later.

function foo(?int $a) {
}

The "Union Types" RFC proposes different syntax, but misses implementation for more than a year. It provides smarter, but less usable (in my opinion) syntax.

function foo(): int|null {
}

Simple “Yes/No” with a 2/3 majority to be accepted.

The vote will start on April 25 and finish on May 9.

https://github.com/php/php-src/pull/1851

After the project is implemented, this section should contain

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

1. "Declaring Nullable Types" RFC
2. "Union Types" RFC
3. Nullable Types in HHVM
4. "Typed Properties" RFC