gistfile1.php

<?php

class Request {

    public function send() {
        
    }

}


// A
$request = new Request();
$request->on('beforeSend', function($request) {
    $signature = new AmazonSignature();
    $signature->sign($request);
});


// B
class AmazonRequest {

    public function sign() {
        $signature = new AmazonSignature();
        $signature->sign($this);
    }

    public function send() {
        $this->sign();
        return parent::send();
    }

}