Interface Not Found

Why This Happens

This error is similar to class not found but specifically for interfaces. It occurs when a class tries to implement an interface that PHP cannot locate. The causes are the same: wrong namespace, missing use statement, or autoloader misconfiguration.

The Problem

namespace App\Service;

class UserService implements Loggable { // Missing use statement
    // ...
}

The Fix

namespace App\Service;

use App\Contract\Loggable;

class UserService implements Loggable {
    // ...
}

Step-by-Step Fix

1. 1

   Check the interface name

   Verify the fully qualified interface name matches the namespace and interface declaration in the source file.

2. 2

   Add the use statement

   Add a use statement at the top of the file to import the interface from its correct namespace.

3. 3

   Verify autoloading

   Ensure the interface file exists at the path Composer expects based on PSR-4 mapping, and run composer dump-autoload.