Simple PHP Object-Oriented $this

Question

I'm trying to brush up on some object oriented basics. I wrote this simple script but am confused as to why it works the way it does.

class Foo
{
function run($text = null)
{
    $this->bar = strtolower($text);
    echo $this->bar;    
}
}

$foo = new Foo;
$foo->run('THIS IS SOME TEXT IN LOWER CASE');

The script outputs "this is some text in lower case" as expected.

But what i'm confused about is why I can do this without actually declaring the $bar variable. Why can I just use $this->bar? Maybe i'm not understanding how $this works properly, but I always thought you had to declare a variable prior to using it in the class. For example public $bar;

Thanks for any insights you may have.

hek2mgl · Accepted Answer · 2013-12-06 22:33:04Z

3

PHP will auto-declare object variables as public if you are accessing them without declaring them as class members before. This is no magic, just a "feature" ;)

However, a good design should not use this "feature" but declare any class members explicitly. Your class should look like this:

class Foo
{
    /**
     * some description
     *
     * @var <type>
     */
    protected $bar;

    ...    

    function run($text = null)
    {
       $this->bar = strtolower($text);
       echo $this->bar;    
    }
}

answered Dec 6, 2013 at 22:33

hek2mgl

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7 Comments

hek2mgl Over a year ago

You asked about the reasons why you should declare a public variable if it will auto declared anyway. There are a few reasons why this makes sense. Once is the the clarity of code, the other that comes in mind are reflectional tasks.

Mitch Over a year ago

Yes that makes sense, I deleted my prior comment because you basically answered it when you edited your answer and mentioned the "good design" aspect.

hek2mgl Over a year ago

As a good advice, I would declare any class member as protected unless there is a proper reason for making it public

bitWorking Over a year ago

The concept of dynamic properties are called Overloading in PHP.

Overloading in PHP provides means to dynamically "create" properties and methods. These dynamic entities are processed via magic methods...

. And overloading makes sense in some cases, too.

hek2mgl Over a year ago

@redreggae Your comment does not fully apply here, as overloading will happen for previously declared protected in the same way as for undeclared members

|

Terry Harvey · Accepted Answer · 2013-12-06 22:37:42Z

0

You can declare variables in a class (a.k.a. properties) like so:

class Foo {
    public $bar;
}

Note the public keyword. Here, we are declaring the property's visibility. There are three types of visibility: public, private, and protected.

public: You can access the property anywhere
private: You can only access the property in the class it's declared in
protected: You can only access the property in the class it's declared in AND any sub-classes

This also applies to methods. I won't go into too much detail, but you can read more here.

If you don't declare a property, but set one in a method like you did in your example, PHP will automatically declare it for you and assign the value you specified.

answered Dec 6, 2013 at 22:37

Terry Harvey

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Comments

SkyHunter · Accepted Answer · 2013-12-06 22:38:29Z

0

You should take a look at http://php.net/manual/en/language.oop5.magic.php

Consider that the same way you declare a variable that did not exist before, out of an object, the same way will happen inside objects, cause they are poorly typed.

answered Dec 6, 2013 at 22:38

SkyHunter

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Comments

StackSlave · Accepted Answer · 2013-12-06 22:47:11Z

0

You would need to put protected, or private in front of your variable outside of your class methods to declare a class variable as anything but public. In PHP assignment is declaration, if it's not already declared. Note, you can also do this:

$ary = array('a', 'b', 'c', 'd');
foreach($ary as $v){
  $newArray[] = $v;
}

Notice, I never declared $newArray = array(); before the loop.

edited Dec 6, 2013 at 22:47

answered Dec 6, 2013 at 22:36

StackSlave

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