What is $this->?

Question

What I think I know so far:

so $this-> is to access a function/var outside its own function/var ?

but how does $this-> know if its a function or a variable ?

why we refer to a var like this $this->data instead of this $this->$data ?

"The pseudo-variable $this is available when a method is called from within an object context. $this is a reference to the calling object (usually the object to which the method belongs, but possibly another object, if the method is called statically from the context of a secondary object). " http://www.php.net/manual/en/language.oop5.basic.php — , Mar 07 '11 at 02:52
possible duplicate of [PHP: self vs. $this](http://stackoverflow.com/questions/151969/php-self-vs-this) — Gordon, Mar 07 '11 at 08:23

score 7 · Accepted Answer · answered Mar 07 '11 at 02:51

7

$this refers to the current object that a method has been invoked on. It knows if it's a function if there is a pair of parentheses at the end. We use the former syntax because $this->$data means look at the field whose name is $data; e.g. $this->foo if $data == 'foo'

answered Mar 07 '11 at 02:51

Edward Z. Yang

26,325
16
80
110

1

I think "whose name is stored in `$data`" would make more sense here. – Dre Mar 07 '11 at 02:52

score 3 · Answer 2 · answered Mar 07 '11 at 02:50

3

$this is the variable referring to the object that you are currently inside. $this-> will access either a method or field in the current object.

As for why is it $this->data and not $this->$data, that's just a syntax quirk. You'd have to ask the PHP language designers. It's probably because the latter wouldn't make much sense for a method.

If this looks like Greek to you, then you may want to head over to the PHP manual's section on classes and objects and read up.

answered Mar 07 '11 at 02:50

Rafe Kettler

75,757
21
156
151

Either "an object" or "instance of a class". If you want to talk about the class itself, you use `self::`. – Billy ONeal Mar 07 '11 at 02:52
Or better yet: '[...] the instance of the class [...]' – phooji Mar 07 '11 at 02:52
@NSanjay are you familiar with object-oriented programming? – Rafe Kettler Mar 07 '11 at 02:53
@NSanjay I find that hard to believe. You've never referred to other methods/fields in a class? – Rafe Kettler Mar 07 '11 at 03:00
ya that's why my first coding was messy until someone pointed it out to me by rewriting it using $this->, & that's how I came to ask this question. So my first post is correct ? – NSanjay Mar 07 '11 at 03:15

score 1 · Answer 3 · answered Mar 07 '11 at 02:52

$this represents the instance of a given object, from the context of within the object.

I would say, knowing whether you're accessing a method or property is your responsibility. Read documentation. If you're calling an object method using this, it uses the expected syntax of $this->method($args); and properties (member variables) use the expected syntax of $this->var = 'value';

score 0 · Answer 4 · answered Mar 07 '11 at 02:51

0

It's a pretty long subject, but in sort, $this is a pointer to an instance. $this->data refers to the data variable of a particular instance(this instance). It is $this->data and not $this->$data just because of convention.

answered Mar 07 '11 at 02:51

Spyros

46,820
25
86
129

so its just a security thing ? – NSanjay Mar 07 '11 at 02:54
No, it has nothing to do with security, take a look at object oriented programming. – Spyros Mar 07 '11 at 03:08
it's a way to refer to the particular object. You'd have to take a look at classes and oop to understand more. – Spyros Mar 07 '11 at 03:22
using $this-> we can nest function within functions ? wont this complicate the reader ? as in the person who want to modify the code later on – NSanjay Mar 07 '11 at 03:32

What is $this->?

4 Answers4