为什么我会使用OOP来隐藏信息？

Question

Why would I use PHP to Hide Information?

<?php

function foo($bar) {
    echo $bar;
}

foo('foobar');

?>

VERSUS

<?php

class foo {
    private $bar;

    function __construct($b){
        $this->bar = $b;
    }

    function display() {
        echo $this->bar;
    }
}

$foobar = new foo('bar');
$foobar->display();

?>

Answer 1

You would do this to encapsulate the functionality and protect the using code from change. Take this example:

class Person
{
    protected $legs;

    public function setLegs($number){
         $this->legs = $number;
    }
}

Lets presume we now have some code that uses this class...

if ($_POST['legs'])
{
   $person = new Person;
   $person->setLegs($_POST['legs']);
}

Ofcours you could do this with the following class

class Person
{
   public $legs;
}

$person = new Person; $person->legs = $_POST['legs'];

The problem comes if you need to provide any validation to legs or if you want to make changes later. Let's say you have to make a change to the rules about a person (for example the maximum amount of legs a person can have is ten) - if you havent encapsulated the logic you now need to go all over your app finding its uses...

class Person
{
    protected $legs;

    public function setLegs($number){ 
         if ( ! is_int($number) || $number > 10){
              throw new Exception('incorrect user input');
         }
         $this->legs = $number;
    }
}

Encapsulation is important for the following reasons:

1. It allows application logic to be reused
2. It makes it possible to make changes easier later