How to make PHP libraries loosely coupled? [closed

问题:

I have some libraries in my 'framework' like routing, config, logger,... I want them to be independent of each other, like some of well known PHP frameworks make them.

I understand all the principles of loose coupling, but I have no clue how to follow both loose coupling and DRY principles. If I make routing library that config and logger, then I don't repeat myself, but if I want to use router on its own it won't work. Similarly if I write logging and config code into my routing library, I would repeat myself.

回答1:

Loose coupling normally means that your components do not expect a concrete instance but just one instance that has a compatible interface.

Each collaborator can be replaced then with a different one of the same type. The code is not dependent on a concrete implementation of one of those any longer.

So:

• Do not use:

  • global (static) functions

    Foo:bar();
    

  • class based programming (passing a classname around)

    stream_wrapper_register("var", "VariableStream");
    

  • global constants

    if ( !defined('ABSPATH') )   
        define('ABSPATH', dirname(__FILE__) . '/');
    

• But:

  • Use objects

    $foo->bar();
    

  • Program against interfaces

    public function __construct(LoggerInterface $logger) {
    

  • Unit-test with mocks

    $logger = $this->getMock('LoggerInterface', array('log'));
    

See as well:

• Don't be STUPID: GRASP SOLID! (Dec 2011; by NikiC)