PHP RFC: get_class() disallow null parameter

Version: 1.0
Date: 2016-08-12
Author: Danack
Status: Implemented (in PHP 7.2)
First Published at: https://wiki.php.net/rfc/get_class_disallow_null_parameter

Introduction

When null is passed as the parameter to get_class() inside a class context, the behaviour of the function can be highly surprising,

class Foo
{
    function bar($repository)
    {
        $result = $repository->find(100);
 
        echo get_class($result);
    }
}

If $result contains a valid object returned from the repository, the output will be of the class name of the type of $result.

If $result contains null, the output will be of the class context where get_class() was called from, in this case “Foo”.

This feature violates the Principle of least astonishment: “if a necessary feature has a high astonishment factor, it may be necessary to redesign the feature.”

Proposal

Disallow null being passed to the function as a valid parameter. If get_class() is called with null as the parameter, a warning will be emitted:

Warning: get_class() expects parameter 1 to be object, null given in %s on line %d

I.e. the valid ways to call the function will be:

without any parameter.
with an object as the parameter.

Those two options will continue to have the same behaviour they currently have.

Backward Incompatible Changes

Most people won't see a BC break, as for the majority of people, passing null to this function is not a desired behaviour.

For people who do deliberately pass null to the function they will need to refactor their code from:

$x = get_class($some_value_that_may_be_null);

to:

if ($some_value_that_may_be_null === null) {
    $x = get_class();
}
else {
    $x = get_class($some_value_that_may_be_null);
}

Proposed PHP Version(s)

7.2

Voting

Should the get_class() function be changed to disallow null being passed as a parameter? As it is not a language or syntax change, the vote will pass if 50%+1 vote yes.

get_class() disallow null parameter
Real name	Yes	No
ajf (ajf)
bishop (bishop)
bwoebi (bwoebi)
colinodell (colinodell)
danack (danack)
daverandom (daverandom)
galvao (galvao)
kguest (kguest)
leigh (leigh)
lstrojny (lstrojny)
malukenho (malukenho)
mariano (mariano)
mike (mike)
mrook (mrook)
ocramius (ocramius)
peehaa (peehaa)
stas (stas)
trowski (trowski)
Final result:	15	3
This poll has been closed.

Voting ended on the 8th October 2016 9pm UTC

null vs default param

When this topic was discussed before, it came as a surprise to some people that PHP can tell the difference between passing null and having a default value be null. This is perfectly possible in both internal code, as well as userland code:

function get_class($item = null)
{
    if (func_num_args() == 0) {
        return get_current_scope_name();
    }
    if ($item === null) {
        trigger_error("get_class passed null, which is not an object.");
    }
 
    if (is_object($item) == false) {
        trigger_error("value is not an object");
        return false;
    }
 
    return gettype($item);
}

Patches and Tests

https://github.com/php/php-src/pull/2082

Implementation

After the project is implemented, this section should contain