PHP OOP Logger example

log_oop_example.php

<?php

interface ICanLog {
 public function writeLine($line);
}

class FileLogger implements ICanLog { //Now I have to implement writeLine!
 private $where;
 public function __construct($where) {
  $this->file = $where;
 }
 public function writeLine($line) {
  file_put_contents($this->where, $line . "\n", FILE_APPEND);
 }
}

class TestLogger implements ICanLog {
 public function writeLine($line) {
  //Do nothing, it's a test logger!
 }
}


/*
As you can see, this log function doesn't know about
the existance of either the FileLogger or TestLogger
I can add any number of loggers I want without 
changing the log function as long as they implement
the ICanLog interface.
*/
function log(ICanLog $logger, $line) {
 $logger->writeLine($line); //I don't know here which logger I'm handed, but I'm sure it'll have writeLine.
}