我无法使用psr-4自动加载课程

Question

I am learning auto loading my calss using psr-4 but I have no luck,here is my folder structure

Here is the code inside my "Employee.php"

   namespace app\Employee;


class Employee
{
   public function __construct(){
       echo "hello employee";

   }

}

and in my index.php

use app\Employee;


  $emp = new Employee;

Here is my composer.json

{
  "autoload": {
    "psr-4": {
       "Employee\\":"app/Employee"
    }
  }
}

Answer 1

Your current autoloader, expects that the "Employee" namespace is mapped within the "app/Employee/" directory.

With your setup, you would need to add in index.php

use Employee\Employee;

$emp = new Employee();

And the actual namespace of Employee.php would be:

namespace Employee;

class Employee {}

Answer 2

Change

use app\Employee;

$emp = new Employee;

to:

use Employee\Employee;

$emp = new Employee();

Answer 3

From your code in Employee.php :

namespace app\Employee;

This is the namespace you have to use if you want to access the class.

PSR-4 in Composer works like this:

"autoload":{"psr-4": { "Namespace\Prefix":"a/path"}}

When loading a class "Namespace\\Prefix\\Class", Composer will see the PSR-4 entry and compare if the class being loaded starts with that Prefix. It does! Now it remove the detected prefix from the classname, and treats the rest as a path and file name relative to "a/path".

So the remainder of that class is "Class", and because there is no backslash left, this directly is the filename "Class.php" (note the uppercase filename). This file is searched in "a/path/Class.php".

For your situation, you almost did everything right - the only thing: Your namespace prefix in composer.json is not Employee\\ - you gave the correct prefix in your code above.