oop - How to make PHP libraries loosely coupled? -

i have libraries in 'framework' routing, config, logger,... want them independent of each other, of known php frameworks make them.

i understand principles of loose coupling, have no clue how follow both loose coupling , dry principles. if make routing library config , logger, don't repeat myself, if want use router on own won't work. if write logging , config code routing library, repeat myself.

loose coupling means components not expect concrete instance 1 instance has compatible interface.

each collaborator can replaced different 1 of same type. code not dependent on concrete implementation of 1 of longer.

so:

• do not use:

  • global (static) functions

    foo:bar(); 

  • class based programming (passing 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 mocks

    $logger = $this->getmock('loggerinterface', array('log')); 

see well:

• don't stupid: grasp solid! (dec 2011; nikic)