PHP, error set static variable for class instance inside class

Question

I'm trying call class method inside another class.

<?php
class A {
    public static $instant = null;
    public static $myvariable = false;

    private function __construct() {}

    public static function initial() {
        if (static::$instant === null) {
            $self = __CLASS__;
            static::$instant = new $self;
        }
        return static::$instant; // A instance
    }
}

class B {
    private $a;

    function __construct($a_instance) {
        $this->a = $a_instance;
    }

    public function b_handle() {
        // should be:
        $this->a::$myvariable = true;
        // but:
        // Parse error: syntax error, unexpected '::' (T_PAAMAYIM_NEKUDOTAYIM)

        // try with:
        // $this->a->myvariable = true;
        // but:
        // Strict Standards: Accessing static property A::$myvariable as non static
    }
}

// in file.php
$b = new B(A::initial());
$b->b_handle();

var_dump(A::$myvariable);

for now, my alternative is:

<?php
class A {
    public function set_static($var,$val) {
        static::$$var = $val;
    }
}

so:

$this->a->set_static('myvariable',true);

what should I do ? what is happen ? am I wrong ?

why I cannot set myvariable as static variable direcly from B class ?

sorry for bad english.

This is highly unusual code, and I think there are several issues here that are confusing you and other possible answerers here. Try putting this into your __construct() method for B and you'll see one of several problems immediately: var_dump($a_instance); I get NULL printed out, so your code does not do what you think it does. — TwoStraws
– TwoStraws, Commented Dec 20, 2015 at 16:29
$myvariable is a static property. Which is assigned using a classname:: syntax. — u_mulder
– u_mulder, Commented Dec 20, 2015 at 16:33
And static::$instant !== null - so if it's NOT null you create new one. And if it's null you just return null? Are you sure? — u_mulder
– u_mulder, Commented Dec 20, 2015 at 16:35
oh, sorry wrong code in A::initial(), should be if (static::$instant === null) — anovsiradj
– anovsiradj, Commented Dec 20, 2015 at 16:35

u_mulder · Accepted Answer · 2015-12-20 16:42:15Z

2

Refer to the manual: http://php.net/manual/en/language.oop5.static.php

A property declared as static cannot be accessed with an instantiated class object (though a static method can).

So, you cannot in anyway set static property from class instance.

As an option you can add some setter, which set your static variable:

public function setMyVar($value) {
    static::$myvariable = $value;
}

$this->a->setMyVar(true);

edited Dec 20, 2015 at 16:42

answered Dec 20, 2015 at 16:39

u_mulder

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Comments

Rajdeep Paul · Accepted Answer · 2015-12-20 16:40:30Z

1

Your call,

$this->a::$myvariable = true;

The PHP manual says,

Declaring class properties or methods as static makes them accessible without needing an instantiation of the class. A property declared as static can not be accessed with an instantiated class object (though a static method can).

This is why you are unable to assign static property through an object.

Simply do this:

A::$myvariable = true;

Here's the reference:

Static Keyword

answered Dec 20, 2015 at 16:40

Rajdeep Paul

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1 Comment

anovsiradj Over a year ago

but, in my 'real' code, I using namespace, and i wouldn't re-import (in this case ) A class using 'use'

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