Cannot Redeclare Class

Why This Happens

PHP does not allow two classes with the same fully qualified name. This error occurs when a file defining a class is included multiple times, or when two files in different locations define the same class. It can also happen with misconfigured autoloaders that map multiple files to the same class.

The Problem

require 'src/Entity/User.php';
require 'src/Entity/User.php'; // Loaded again

The Fix

require_once 'src/Entity/User.php';
// Or better: use Composer autoloading and never require manually

Step-by-Step Fix

1. 1

   Find both declarations

   The error tells you where the class was previously declared. Search your codebase for duplicate class definitions with the same name.

2. 2

   Use require_once

   Replace all require and include with require_once and include_once for files that define classes.

3. 3

   Switch to autoloading

   Use Composer's PSR-4 autoloading to automatically load classes based on namespace and directory structure, eliminating manual includes.