PHP CookBook

Recipe 7.11 Finding the Methods and Properties of an Object

7.11.1 Problem

You want to inspect an object to see what methods and properties it has, which lets you write code that works on any generic object, regardless of type.

7.11.2 Solution

Use get_class_methods( ) and get_class_vars( ) to probe an object for information:

// learn about cars
$car_methods = get_class_methods('car');
$car_vars    = get_class_vars('car');

// act on our knowledge
if (in_array('speed_away', $car_methods)) {
    $getaway_van = new car;
    $getaway_van->speed_away( );
}

7.11.3 Discussion

It's rare to have an object and be unable to examine the actual code to see how it's described. Still, these functions can be useful for projects you want to apply to a whole range of different classes, such as creating automated class documentation, generic object debuggers, and state savers, like serialize( ).

Both get_class_methods( ) and get_class_vars( ) return an array of values. In get_class_methods( ), the keys are numbers, and the values are the method names. For get_class_vars( ), both variable names and default values (assigned using var) are returned, with the variable name as the key and the default value, if any, as the value.

Another useful function is get_object_vars( ) . Unlike its sister function get_class_vars( ), get_object_vars( ) returns variable information about a specific instance of an object, instead of a generic newly created object.

As a result, you can use it to check the status of an object as it currently exists in a program:

$clunker = new car;
$clunker_vars = get_object_vars($clunker); // we pass the object, not the class

Since you want information about a specific object, you pass the object and not its class name. But, get_object_vars( ) returns information in the same format as get_class_vars( ).

This makes it easy to write quick scripts to see if you're adding new class variables:

$new_vars = array_diff(array_keys(get_object_vars($clunker)),
                       array_keys(get_class_vars('car')));

You extract the variable names using array_keys( ) . Then, with the help of array_diff( ), you find which variables are in the $clunker object that aren't defined in the car class.

If you just need a quick view at an object instance, and don't want to fiddle with get_class_vars( ), use either var_dump( ) , var_export( ), or print_r( ) to print the object's values. Each of these three functions prints out information in a slightly different way; var_export( ) can optionally return the information, instead of displaying it.

7.11.4 See Also

Recipe 5.9 for more on printing variables; documentation on get_class_vars( ) at http://www.php.net/get-class-vars, get_class_methods( ) at http://www.php.net/get-class-methods, get_object_vars( ) at http://www.php.net/get-object-vars, var_dump( ) at http://www.php.net/var-dump, var_export( ) at http://www.php.net/var-export, and print_r( ) at http://www.php.net/print-r.