rfc:catchable-call-to-member-of-non-object

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PHP RFC: Catchable "call to a member function of a non-object"

Introduction

One of the most common fatal errors in PHP is the “call to a member function of a non-object” type. This occurs whenever a method is called on anything other than an object (usually null), e.g.: 

// ...when getAction() returns null:
$this->getAction()->invoke();

If you want to run PHP as a webserver itself, fatal errors are problematic. For a long story on why you would want to do that in the first place, see http://marcjschmidt.de/blog/2014/02/08/php-high-performance.html

Proposal

This proposal's essence is to turns fatal errors generated from calls to methods on a non-object into E_RECOVERABLE_ERRORs. 

set_error_handler(function($code, $message) {
  var_dump($code, $message);
});
 
$x= null;
var_dump($x->method());
echo "Alive\n";

The above produces the following output: 

int(4096)
string(50) "Call to a member function method() on a non-object"
NULL
Alive

Consistency

This behavior is consistent with how type hints work. Framework authors can turn this into exceptions if they wish.

This proposal adds an optional return type declaration to function declarations including closures, functions, generators, interface method declarations and class declarations. This RFC does not change the existing type declarations nor does it add new ones (see differences from past RFCs).

Example

The following error handler could be embedded into frameworks: 

set_error_handler(function($code, $message) {
  if (0 === strncmp('Call', $message, 4)) {
    throw new BadMethodCallException($message);
  } else if (0 === strncmp('Argument', $message, 8)) {
    throw new InvalidArgumentException($message);
  } else {
    trigger_error($message, E_USER_ERROR);
  }
}, E_RECOVERABLE_ERROR);
 
$x= null;
try {
  $x->method();
} catch (BadMethodCallException $e) {
  echo "Caught expected ", $e->getMessage(), "!\n";
}
echo "Alive\n";

Differences from Past RFCs

This proposal doesn't go as far as the controversial RFC RFC: Engine exceptions.

Other Impact

On Backward Compatiblity

This RFC is backwards compatible with previous PHP releases.

On SAPIs

There is no impact on any SAPI.

On Existing Extensions

No impact.

On Performance

No effect, before, the script terminated.

Proposed PHP Version(s)

This RFC targets PHP 5.7 or PHP 6.0, whichever comes first.

Proposed Voting Choices

This RFC modifies the PHP language behaviour and therefore requires a two-third majority of votes.

Patches and Tests

There is a pull request available over at GitHub which includes tests. Feedback welcome!

Future Work

Ideas for future work include:

  • Also allowing to catch
  • Allowing nullable types(such as ?DateTime). This is discussed in a related RFC: Declaring Nullable Types
  • Unifying the reflection type API by introducing a ReflectionType class that both parameter and return types can use.
  • Improving parameter variance. Currently parameter types are invariant while they could be contravariant.
  • Improving runtime performance by doing type analysis.
  • Updating documentation to use the new return type syntax.

References

rfc/catchable-call-to-member-of-non-object.1398523245.txt.gz · Last modified: 2017/09/22 13:28 (external edit)

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