PHP RFC: Mixed typehint

• Version: 1.0
• Date: 2017-07-19
• Author: Michael Moravec (php.net@majkl578.cz)
• Status: Draft
• First Published at: http://wiki.php.net/rfc/mixed-typehint

With the addition of scalar types in PHP 7, nullables in 7.1 and recently object in 7.2, it's now possible to explicitly declare accepted types for most of the parameters and return types. Unfortunately without mixed type it's still not possible to achieve a fully type hinted and consistent code.

This RFC proposes to add the mixed type to be used for parameter and return types to explicitly declare desired type.

Primary motivation for having explicit mixed type is consistence and easier static analysis. In PHP 7.2, mixed types are unfortunately the only type that could not be type hinted upon (and resource as well, but its future is unclear and usage rare). Having mixed type would allow a code with 100% type coverage in most cases.

The behavior of the mixed type fully matches the behavior when nothing is specified for parameter or return type (thus being implicitly mixed), effectively being an alias.

As the mixed type accepts anything, including null, nullable mixed type (?mixed) is disabled at compile time.

function foo(): ?mixed {}
// Fatal error

No changes to variance needed. Exactly same rules as when no type is present apply.

Since the mixed type and no type are functionally equivalent, the following code is functionally equivalent as well:

function foo($arg) {
    return $arg;
}

and

function foo(mixed $arg): mixed {
    return $arg;
}

Same applies to inheritance, where mixed type and no type could be interchanged without any error. This code would work just fine:

class Foo {
    public function test(mixed $arg): mixed {
        return $arg;
     }
}
class Bar extends Foo {
    public function test($arg) {
        return parent::test($arg);
    }
}
class Baz extends bar {
    public function test(mixed $arg): mixed {
        return parent::test($arg);
    }
}

None, mixed is already reserved since PHP 7.0.

7.2 if RMs agree, otherwise 7.3

None.

None.

None.

No changes to type cast operators.

Simple yes/no vote to either accept or reject addition of mixed type. As this is a language change, 2/3 majority is required.

GitHub Pull request #2063

• PHP RFC: Reserve Even More Types in PHP 7
• phpDocumentor type reference