php - The benefit of static array?

This question already has answers here:

Answer

Solution:

If a attribute is static it can be accessed without creating an instance of this class.

//static
class MyClass(){
        static $lang = array(
            'message' => 'Welcome ',
            'admin' => 'administrator'
        );
}
var_dump (MyClass::$lang)

//public
class MyClass(){
        public $lang = array(
            'message' => 'Welcome ',
            'admin' => 'administrator'
        );
}
$obj = new MyClass();
var_dump($obj->lang);

Static properties are accessed using the Scope Resolution Operator (::) and cannot be accessed through the object operator (->).

A static variable exists only in a local function scope, but it does not lose its value when program execution leaves this scope.

function myFunction()
{
    $nonStatic = 0;
    echo $nonStatic;
    $nonStatic++;
}

myFunction(); // OUTPUT: 0
myFunction(); // OUTPUT: 0
myFunction(); // OUTPUT: 0
myFunction(); // OUTPUT: 0

The function test always returns Zero as the $nonStatic variable lose its value.

While in this function:

function myFunction()
{
    static $staticVar = 0;
    echo $staticVar;
    $staticVar++;
}

myFunction(); // OUTPUT: 0
myFunction(); // OUTPUT: 1
myFunction(); // OUTPUT: 2
myFunction(); // OUTPUT: 3

Because the $staticVar variable is static, so it retain its value.

The same applies to your array

function test()
{
    static $lang = array(
        'message' => 'Welcome ',
        'admin' => 'administrator'
    );

    var_dump($lang);
    $lang['message'] = 'new message ';
}

test(); // OUTPUT: array(2) { ["message"]=> string(6) "Welcome" ["admin"]=> string(9) "administrator" }
test(); // OUTPUT: array(2) { ["message"]=> string(6) "new message" ["admin"]=> string(9) "administrator" }

To access a static variable or method from inside the class you can use the self keyword. To access a static variable or calling a method from a class that is extended by the class containing the static variable you can use the parent keyword

class MyClass{
        static $lang = array(
            'message' => 'Welcome ',
            'admin' => 'administrator'
        );
        static function myFunction(){
            return self::$lang;
        }
}

class ScndClass extends MyClass{
    public function callStaticFunction(){
        var_dump(parent::$lang);
        return parent::$myFunction();
    }
}
$obj = new ScndClass();
echo $obj->callStaticFunction();

Answer

Solution:

Please review this https://www.php.net/manual/en/language.variables.scope.php#language.variables.scope.static https://www.php.net/manual/en/language.oop5.static.php#language.oop5.static.methods https://www.php.net/manual/en/language.oop5.static.php#language.oop5.static.properties

A static variable exists only in a local function scope, but it does not lose its value when program execution leaves this scope.

So in the following example:

    function test()
    {
        $a = 0;
        echo $a;
        $a++;
    }
    
    test(); // OUTPUT: 0
    test(); // OUTPUT: 0
    test(); // OUTPUT: 0
    test(); // OUTPUT: 0

The function test always returns Zero as the $a variable lose its value.

While in this function:


    function test()
    {
        static $a = 0;
        echo $a;
        $a++;
    }
    
    test(); // OUTPUT: 0
    test(); // OUTPUT: 1
    test(); // OUTPUT: 2
    test(); // OUTPUT: 3

Because the $a variable is static, so it retain its value.

Also in array,


    function test()
    {
        static $lang = array(
            'message' => 'Welcome ',
            'admin' => 'administrator'
        );
    
        var_dump($lang);
        $lang['message'] = 'Hello ';
    }
    
    test(); // OUTPUT: array(2) { ["message"]=> string(6) "Welcome" ["admin"]=> string(9) "administrator" }
    test(); // OUTPUT: array(2) { ["message"]=> string(6) "Hello" ["admin"]=> string(9) "administrator" }

In the previous example, the first run will output "Welcome administartor", while the second run will output "Hello administrator".

Also,

Static variables can be assigned values which are the result of constant expressions, but dynamic expressions, such as function calls, will cause a parse error.

so the following example will cause error

$name = "Omar";
static $lang = array(
    'message' => 'Welcome ',
    'admin' => 'administrator' . $name,
);
var_dump($lang); // Fatal error: Constant expression contains invalid operations

While the following code is valid one:

$name = "Omar";
$lang = array(
    'message' => 'Welcome ',
    'admin' => 'administrator' . $name,
);
var_dump($lang); // OUTPUT: array(2) { ["message"]=> string(9) "Welcome " ["admin"]=> string(12) "administratorOmar" }

Also note this:

Static properties are accessed using the Scope Resolution Operator (::) and cannot be accessed through the object operator (->).

It's possible to reference the class using a variable. The variable's value cannot be a keyword (e.g. self, parent and static).

So the following example is valid


    class Foo
    {
        static $lang = array(
            'message' => 'Welcome ',
            'admin' => 'administrator'
        );
    }
    var_dump(Foo::$lang); // array(2) { ["message"]=> string(9) "Welcome " ["admin"]=> string(9) "administrator" }

While the following example will throw fatal error


    class Foo
    {
        public $lang = array(
            'message' => 'Welcome ',
            'admin' => 'administrator'
        );
    }
    var_dump(Foo::$lang); // Fatal error:  Uncaught Error: Access to undeclared static property Foo::$lang

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