PHP, OOP, Static

Question

I am have a problem with undestanding some sentence at PHP.net about the static keyword, At This Link , PHP.net Explaining about the static keyword i did understand all they say but i didn't succeed to get one sentence witch start at "Like any other PHP static variable". I just didn't get it if can some one please help me with code example, mabye explanation will be great.

Answer 1

When saying "like any other static variable" the manual refers to a static variable inside a function. The archetypal example is the function that keeps an internal counter:

function foo() {
    static $counter = 0; // static variable
    return ++$counter;
}

Static variables like this and static class properties both have a limitation on the expressions you can initialize them with.

function foo() {
    static $counter = getInitialValue(); // ERROR: not possible!
    return ++$counter;
}

If you need to do something like this, the usual workaround is

function foo() {
    static $counter; // not initialized explicitly, same as = null
    if ($counter === null) { // three equals!
        $counter = getInitialValue();
    }
    return ++$counter;
}

Answer 2

Basically, you can do this:

class Foo
{
    public static $my_static = 'foo';

    public function staticValue() {
        return self::$my_static;
    }
}

where $my_static is initialise as a string with the value foo . But you can't do:

class Foo
{
    public static $my_static = substr('food',0,3);

    public function staticValue() {
        return self::$my_static;
    }
}

and expect $my_static to contain the results of the function call to substr ; directly assigning a function's return value to a static variable is an illegal operation. Similarly, you can't do:

class Foo
{
    public static $my_static = 'foo';
    public static $my_static_2 = $my_static;

    public function staticValue() {
        return self::$my_static;
    }
}

because you may not initialise a static variable by pointing to another variable.