在PHP中替代全局

Question

Global variables are generally considered bad practice unless absolutely necessary, so I am looking at alternative ways to achieve some functionality.

We are currently working on a CMS system in PHP, and wish to allow other developers to write modules easily for the CMS. We have defined a CMS class as follows:

class CMS
{
    public $version;
    public $sitename;
    public $siteurl;
    public $tbl_prefix;

    function __construct()
    { 

    }

    function RegisterModule()
    {

    }
}

Now, we would like to generate an instance of CMS, and make it accessible to the developer (and all modules and core files) through a variable: $_cms. Since we are not able to use constant variables for objects in PHP, and using a Singleton pattern provides clumsy syntax to access the instance (i.e. CMS::GetInstance()->RegisterModule()), is there any way to achieve what we want without defining a global variable containing an instance of CMS?

Ideally, we are looking for something like the following syntax:

_cms->RegisterModule(); or $_cms->RegisterModule();, with the former being preferred.

Answer 1

Require plugins to be coded as classes, which either extend the CMS class or accept it as a parameter to their constructor. That's also known as Dependency Injection and is just about the cleanest interface you can get.

class MyPlugin {

    public function __construct(CMS $cms) {
        ...
    }

}

Requiring plugins to be classes also makes it really clean and easy to include them from your app, since they're self-contained and can easily follow specific naming and interface conventions.