CODEWITHSUNDEEP
phpdynamicmethodsstatic
user3569859
user3569859

Reputation: 11

Static variable inside PHP dynamic method

Why there are static variables inside dynamic methods in PHP? I supposed to use static to store value between method calls, but discovered that static vars are just like static fields (members) of class.

class A {
    public function B() {
        static $C;
        if (!isset($C) {
            $C = rand();
        }
        echo $C."\n";
    }
}

$i1 = new A;
$i1->B();

$i2 = new A;
$i2->B();

What is the best way to store value (cache it) between method's call?

Upvotes: 1

Views: 557

Answers (2)

Halcyon
Halcyon

Reputation: 57709

A static variable is similar to a static member. One minor difference is that it's scoped to the function you've declared it in.

Keep in mind that static members have one other property: they are shared over all instances of a class. Sample code:

class A {
    function foo () {
        static $a = 0;
        $a += 1;
        var_dump($a);
    }
    function bar() {
        self::$a; // Fatal error: Access to undeclared static property: A::$a
    }
}

$a = new A();
$a->foo(); // 1
$a->foo(); // 2
$a2 = new A();
$a2->foo(); // 3!

This is problematic. My recommendation is: don't use static variables. Just have a private non-static member:

class A {
    private $a = 0;
    function foo () {
        $this->a += 1;
        var_dump($this->a);
    }
}

$a = new A();
$a->foo(); // 1
$a->foo(); // 2
$a2 = new A();
$a2->foo(); // 1

If you need to cache a value make that it's own entity:

$cache = new ValueProvider();
$a = new A($cache);
$a2 = new A($cache);

Now A doesn't need to know how ValueProvider get's the value, or even that it's cached. $a and $a2 share their ValueProvider, but they don't know about that, and that's good.

Upvotes: 3

Kryten
Kryten

Reputation: 15760

In the code you've given, the variable $C maintains it's value between successive calls to function B(). It is also private to the function B(). Note, however, that it is truly static - every instance of A will have the same value of $C in it's method B.

The best way to store the value? That depends on what you're using it for:

  1. If you need the value to be private to method B and you don't mind having the same value of $C for every instance of A, then this is the way to go.
  2. If you need the value to be unique to every instance of A, then make it a (private) member variable (although in this case, it will be accessible from every method of A).

Upvotes: 0

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