php - understanding the parameters passed to the array_reduce method -

i going through this online tutorial, , see below script:

<?php  include_once 'renderer.php';  class page {      protected $renderers;      public function add($renderer) {         $this->renderers[] = $renderer;     }      public function render() {          $content = '';         $content .= "--start of page--\n";         $content .= array_reduce($this->renderers , function($output , $r){             return $output .= $r->render()."\n";         } , '');         $content .= "--end of page--\n";          return $content;     }  }  $page = new page();  $page->add(new blogrenderer()); $page->add(new articlerenderer());  echo $page->render(); 

lets zoom in the call array_reduce() call,

 $content .= array_reduce($this->renderers , function($output , $r){                 return $output .= $r->render()."\n";             } , ''); 

i have 2 funcdamental questions here, there 2 parameters being passed array_reduce function , when did render() become property of $r , call $r->render() valid ? how on earth call valid ?

i have seen php manual on array_reduce method , way method gets used here baffles me, can explain , answer above questions , grateful .

thank you.

alex-z.

what there 2 parameters being passed array_reduce function?

the first parameter array 2 elements (an instance of blogrenderer() , instance of articlerenderer()).

the second parameter callback function.

when did render() become property of $r?

the callback has 2 parameters, second parameter $r holds value of current iteration. instance of blogrenderer() or articlerenderer() in classes blogrenderer() , articlerenderer() there method called render()

i hope makes sense.