PHP empty() on __get accessor

Question

Using PHP 5.3 I'm experiencing weird / non-intuitive behavior when applying empty() to dynamic object properties fetched via the __get() overload function. Consider the following code snippet:

<?php  class Test {    protected $_data= array(    'id'=> 23,    'name'=> 'my string'   );    function __get($k) {     return $this->_data[$k];   }  }  $test= new Test(); var_dump("Accessing directly:"); var_dump($test->name); var_dump($test->id); var_dump(empty($test->name)); var_dump(empty($test->id));  var_dump("Accessing after variable assignment:"); $name= $test->name; $id= $test->id; var_dump($name); var_dump($id); var_dump(empty($name)); var_dump(empty($id));  ?> 

The output of this function is as follow. Compare the results of the empty() checks on the first and second result sets:

Set #1, unexpected result:

string(19) "Accessing directly:" string(9) "my string" int(23) bool(true) bool(true) 

Expecting Set #1 to return the same as Set #2:

string(36) "Accessing after variable assignment:" string(9) "my string" int(23) bool(false) bool(false) 

This is really baffling and non-intuitive. The object properties output non-empty strings but empty() considers them to be empty strings. What's going on here?

Answer 1

Based on a reading of the empty's manual page and comments (Ctrl-F for isset and/or double underscores), it looks like this is known behavior, and if you want your __set and __get methods and empty to play nice together, there's an implicit assumption that you implement a __isset magic method as well.

It is a little bit unintuitive and confusing, but that tends to happen with most meta-programming, particularly in a system like PHP.