How to make a function in php in modx or something else?

Question

PHP

Hello, help me figure out how the functions in php work, or maybe something else is needed here.
There is a code:

if (true) {
  $bd_user = $modx->newObject('User');
  $bd_user->set('fullname', $_POST['name']);
  $bd_user->set('email', $_POST['email']);
  $bd_user->save();
} else {
  $id = $_SESSION['id'];
  $bd_user = $modx->getObject('User',array('id'=>$id));
  $bd_user->set('fullname', $_POST['name']);
  $bd_user->set('email', $_POST['email']);
  $bd_user->save();
}

This is a sample code. There is a repeating part in the code, tell me how and where you can stuff this repeating code so that it is only in one place.
I tried functions, but something does not work. Gives an error message

Fatal error: Cannot redeclare

Answer 1

Created a class helped

Answer 2

create a snippet, of course
Cannot redeclare says that a function with that name already exists