A forced class that implements an interface for defining a constant

Question

I am ready to force my classes to define a constant named COMMAND. If php would allow you to redefine constants from interfaces, it would look like

class RequestInterface { const COMMAND = "no-command-specified"; } class LoginRequest implements RequestInterface { const COMMAND = "loginuser"; public $username; public $password; } $request = new LoginRequest(); $request->username = "user"; $request->password = "blah"; 

Obviously this does not work. I am looking for a clean way for my queries to define COMMAND cosntant.

I considered the following options:

• The interface defines the getCommand method, and my request classes should implement it and return the command name as a string. But this is too much code to query
• Replace the interface with an abstract class. This looks strange because it usually requires an abstract class to define at least one method.

• The interface becomes an abstract class and defines the protected variable $ command. It also has a getter method that returns $ this-> command ;. Children override the $ command protected property. I don't like the way mixing public VARIABLES (which should be a variable) with the protected variable VARIABLE, which in fact should not be modifiable and therefore should not be considered a variable in the first place.

   class LoginRequest extends BaseRequest { protected $command = "loginuser"; public $username; public $password; } 

What will be the cleanest way to achieve this?

Answer 1

Personally, my choice:

 interface RequestInterface { /** * @returns string */ public function getCommand(); } class LoginRequest implements RequestInterface { public function getCommand() { return "loginuser"; } ... } 

You can always check that the string will be returned with is_string() later. There is nothing stopping anyone from setting COMMAND to a number.