<?php

interface AccessControl
{
  public function userCan($action);
}

class BitmaskAccessControl implements AccessControl
{
  public function userCan($action)
  {
    // bitmask comparison here based on $action
    // return bool
  }
}

class SomeOtherAccessControl implements AccessControl
{
  public function userCan($action)
  {
    // some other type of comparison you have implemented
    // that does not use bitmask
    // return bool
  }
}

// When I ask for AccessControl give me the bitmask implementation
$app->bind('AccessControl', 'BitmaskAccessControl');

// Later on you decide to use your new implementation
// When I ask for AccessControl give me the other implementation
$app->bind('AccessControl', 'SomeOtherAccessControl');

// Now none of your code other than
// the one line above needs updated even when completely removing the bitmask stuff