Avoid This In Static

ID

php.avoid_this_in_static

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Php

Tags

object-context, reliability

Description

Reports a use of the $this pseudo-variable inside a method declared static (directly, or within a closure declared in that static method). A static method has no object context, so $this is unbound.

Rationale

$this refers to the current object instance. A static method is invoked on the class itself, with no instance, so $this is undefined there; dereferencing it raises a fatal Error: Using $this when not in object context. The same applies to a closure created inside a static method: it has no instance to bind, plain or static. Catching this at review time prevents a crash that only surfaces at runtime when the static method is actually called.

<?php
class Registry
{
    private string $name = 'default';

    public static function create(): string
    {
        return $this->name;        // FLAW — static method, $this is unbound
    }

    public static function build(): callable
    {
        return function () {
            return $this->name;    // FLAW — closure in a static method has no $this either
        };
    }

    public function instance(): string
    {
        return $this->name;        // OK — instance method, $this is valid
    }
}

Remediation

If the member belongs to an instance, make the method non-static and call it on an object. If the method is genuinely class-level, replace $this→member with the static form (self::$property, static::method()) or pass the needed value in as a parameter.

References