When should I use Static functions/classes/fields in PHP? What are some practical uses of it?
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3If you are trying to write object oriented code: NEVER.tereško– tereško2012-08-11 21:57:56 +00:00Commented Aug 11, 2012 at 21:57
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3 Answers
you should not, it's rarely useful. common usage for statics are factory methods and singleton::instance()
factory:
class Point{
private $x;
private $y;
public function __construct($x, $y){
...
}
static function fromArray($arr){
return new Point($arr["x"], $arr["y"]);
}
}
singleton:
class DB{
private $inst;
private function __construct(){
...
}
static function instance(){
if ($this->inst)
return $this->inst;
return $this->inst = new DB();
}
}
3 Comments
koen
I agree it's mostly not necessary and harmful. I would add one case where it is usefull: to create a higher level language. Eg User::with100Points(). More can be found in the book Growing object oriented software guided by tests.
Ali
@koen explain a bit more, how would User::with100points() work?
koen
@Click Upvote If you mean how it looks in code: class User { public function setPoints($points) { //set points } public static function with100points() { return new self(100); } }. User::with100points() is more readable than $user = new User(); $user->setPoints(100); You could create a special class for this DSLUser extends User { public static method with100points() {} }. There aren't that many opportunities to use this correctly in your code but in UnitTests you can make more use of it and your tests often become very clear.
Usage of static methods in same in languages like Java/PHP.
One simple example can be that you want to use a variable across all instances of your class and any instance can change its value and you want it to get reflected in other instance as well.
class Foo{
static $count=0;
public function incrementCount(){
self::$count++;
}
public function getCount(){
return self:$count;
}
}
Without static you can't set count value via one object and access it in others.
Comments
I occasionally use STATIC Methods when I need simple functions in a Class that I also use outside the Class such as:
in a UserProfile class I have an method that returns an array that is used to pass data back to the class after the array is populated from the html page.
Class UserProfile{
Public Static get_empty_array(){
return array('firstname'=>'',lastname=>''); //usually much more complex multi-dim arrays
}
}
This way the empty array can be used within the class/object and outside as a starting template. I also use Static Methods for functions that would normally be standalone functions but I want to keep them in the class so it is all together but also make them available outside as a static method such as:
public static convert_data($string){
//do some data conversion or manipulating here then
return $ret_value;
}
$converted_data = class::convert_data($string);
I do maintain an library of common user defined functions but I have found it handy to include some in the class to which it is closely related.
