Why Can\'t I Call Non-Static Methods Using the Double-Colon Syntax in PHP?

Calling Non-Static Methods with Double-Colon Syntax

In PHP, static methods can be invoked using the class name followed by the scope resolution operator (::). However, it's generally not possible to call non-static methods in the same manner.

Non-Static Methods with Double-Colon Syntax

The code snippet below attempts to call a non-static method, fun1, using the double-colon syntax:

class Teste {

    public function fun1() {
        echo 'fun1';
    }
    public static function fun2() {
        echo "static fun2" ;
    }
}

Teste::fun1(); // why?
Teste::fun2(); // ok - is a static method

This code will result in an error, as non-static methods cannot be accessed directly through the class name.

Reason for Restriction

PHP employs loose typing for static vs. non-static methods. When a non-static method is called statically, the $this keyword inside that method will not refer to an instance of the class. This loose behavior can lead to inconsistent and potentially erroneous code.

Static Method Variants

The double-colon syntax is only permissible for calling static methods. Here's an example:

class StaticExample {

    public static function staticMethod() {
        echo "static method";
    }
}

StaticExample::staticMethod(); // valid

Within Non-Static Methods

It's possible to call a non-static method statically from within a non-static method of the same class. In such cases, $this inside the called method will still refer to the correct object instance.

class A {

    public function nonStaticMethod() {
        echo $this->name;
    }
}

class C {

    public function callNonStatic() {
        $this->name = 'Example';
        A::nonStaticMethod(); // valid
    }
}

$c = new C;
$c->callNonStatic(); // prints Example

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