When to use static methods/fields in PHP?

W开发者_StackOverflowhen should I use Static functions/classes/fields in PHP? What are some practical uses of it?

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();
  }
}

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.

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.