Using self:: instead of $this

Question

i came by some php code where the developer who wrote it is being a little contradictory i think. so here is the code he wrote:

if ($this->SQL !== null && $this->SQLState === self::STATE_CLEAN)
        return $this->SQL;

where the SQLState and the STATE_CLEAN are defined like this:

class someClass {
    const STATE_CLEAN = 1;
    private $SQLState = self::STATE_CLEAN;
}

so you can see that for some class attributes he uses $this and for some he uses self:: and i can't understand why. can any one help. Thanks

Possible duplicate of [When to use self over $this?](https://stackoverflow.com/questions/151969/when-to-use-self-over-this) — Spoody, Apr 13 '18 at 21:58
not possible because i know what they both mean, i just don't understand this specific case. — oajmi, Apr 13 '18 at 22:00
Guess I don't understand your question then. Can you explain more? — Spoody, Apr 13 '18 at 22:01
he is purposely using both self:: and $this while he can use $this instead, actually he should use none of the defined attributes are static? so i think either he is inconsistent with his code or he knows something i don't know — oajmi, Apr 13 '18 at 22:04

Don't Panic · Accepted Answer · 2018-04-13T22:19:04.117

3

Here:

private $SQLState = self::STATE_CLEAN;

The property is initialized to the value of the constant.

At some point, the property may change, but the constant is constant. So checking for this condition:

$this->SQLState === self::STATE_CLEAN

makes sense to verify that the current state is the same as the initial state.

To clarify since I think I missed the main point of the question, self::STATE_CLEAN is used because STATE_CLEAN is a class constant. Using $this->STATE_CLEAN will get you

Notice: Undefined property: someClass::$STATE_CLEAN

edited Apr 13 '18 at 22:19

answered Apr 13 '18 at 22:01

Don't Panic

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why not using $this->STATE_CLEAN instead of self::STATE_CLEAN – oajmi Apr 13 '18 at 22:06
@Dever In which part he should've used `$this->STATE_CLEAN` instead of `self::STATE_CLEAN`? – Spoody Apr 13 '18 at 22:12
both actually while none of them are static why using self:: – oajmi Apr 13 '18 at 22:13
@Dever `STATE_CLEAN` is a constant, you can't access it using `$this` – Spoody Apr 13 '18 at 22:15

score 1 · Answer 2 · answered Apr 13 '18 at 22:30

1

Good practice is to:

use self:: for class constants
(when refering class - you could have no initialized object instance of this class)

and $this-> for class variables
(when refering initialized object instance)

answered Apr 13 '18 at 22:30

mu4ddi3

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10

Using self:: instead of $this

2 Answers2