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();

One situation in which fatal errors are problematic is if you want to run PHP as a webserver itself. 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.

Other situtations are described in the Engine Exceptions RFC.

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.

Example: Exceptions

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";

Example: Without exceptions

This could be a way for people preferring not to use exceptions and instead to exit the script directly, but get a stacktrace instead of just the fatal error message:

set_error_handler(function($code, $message) {
  echo "*** Error #$code: $message\n";
  debug_print_backtrace();
  exit(0xFF);
}, E_RECOVERABLE_ERROR);
 
$m= new some_db_model();
$row= $m->find(42); // null, deleted concurrently
$row->delete();

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 and handle other fatal errors

References

rfc/catchable-call-to-member-of-non-object.1398646973.txt.gz · Last modified: 2017/09/22 13:28 (external edit)