CODEWITHSUNDEEP
phpconstants
abuduba
abuduba

Reputation: 5042

Redefining constants in PHP

Is it possible to redefine a constant in php which was defined by the define function? I have a class with several constants that contains the user data. I'm trying to use the class for more than one user.

define('ALLEGRO_ID', 'id');
define('ALLEGRO_LOGIN', 'login');
define('ALLEGRO_PASSWORD', 'passwd');
define('ALLEGRO_KEY', 'key');
define('ALLEGRO_COUNTRY', 123);

$allegro = new AllegroWebAPI( );                
$allegro -> Login();

I did not write this class, but I am using it due to time constraints. I do not know why the creator of this class defined the user data rather than using the variables in the instance.

I know that constants should be constant (obviously!), but I'm looking for a trick to redefine them.

Upvotes: 46

Views: 82818

Answers (5)

Ronak Dhoot
Ronak Dhoot

Reputation: 2321

passing 3rd param as true will help you

define('CONSTANT_NAME', 'constant_value', true);
print CONSTANT_NAME.PHP_EOL;
define('CONSTANT_NAME', 'constant_value2');
print CONSTANT_NAME.PHP_EOL;

https://ideone.com/oUG5M9

Upvotes: 6

Dereckson
Dereckson

Reputation: 1421

In PHP 5.6+, you can import constants, under an alias. Such alias can overwrite an already existing constant.

The following snippet will print int(5):

define('ALLEGRO_ID', 3);
define('NEW_ALLEGRO_ID', 5);
use const NEW_ALLEGRO_ID as ALLEGRO_ID;
var_dump(ALLEGRO_ID);

Such mechanism could be legitimate in unit test, or other areas where magic behavior is tolerated, but isn't convenient for your use case, where a class to store your user settings would be more useful.

Finally, this behavior allows to create very confusing situations like use const true as false;.

Upvotes: 23

atif
atif

Reputation: 87

Constants value once defined remains unchanged throughout the program. If you have such a requirement where you want to change the values in future then keep such values in PHP variables.

Upvotes: 4

ajreal
ajreal

Reputation: 47331

No, you cannot redefine a constant (except with runkit_constant_redefine),
that's why is called CONSTANT.

What you are looking for in the class is actually an object variable in array format:-

class user
{
  public $user = array();

  function load($user_id)
  {
    // etc
    $this->$user[$user_id] = something_else;
  }
}

Upvotes: 25

user142162
user142162

Reputation:

If you have the runkit extension installed, you can use runkit_constant_redefine():

runkit_constant_redefine("name", "value");

In most circumstances, however, it would be a better idea to re-evaluate why you're using constants and not something more fitting.

Upvotes: 60

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