Need PHP related clarification - php

Question

I have the following code written in a file name "backend_user.php"
CODE 1:
<?php
require_once '_db.php';
$json = file_get_contents('php://input');
$params = json_decode($json);
class Result {}
$response = new Result();
if ($user != null) {
$response->result = 'OK';
$response->user = $user['name'];
$response->message = 'Success';
}
else {
$response->result = 'Unauthorized';
$response->message = 'Invalid token';
}
header('Content-Type: application/json');
echo json_encode($response);
?>
The above code gets called by the code below stored in data.service.ts in Angular
CODE 2:
getUser(): Observable<any> {
return this.http.post("/api/backend_user.php", {}).pipe(map((response:any) => {
this.user = response.user;
return response;
}));
}
As you can see from above code, nothing gets passed in the request body. But in CODE 1, there is a variable named $user referred.
From where does $user get it's value from?
Can somebody clarify?

Answer 1

$user is just the response value. It's kind of like an arrow function in javascript so you can rename $user to $foo and do $foo['name'] and it will still work.
$user is just the given variable name for the response. So, $user['name'] is accessing HttpResonse.name effectively. name is just a property on the response.