example trait doing heavy lifting in 8.2

serialize-trait.php

<?php
trait Serialize {
    public function jsonSerialize(): array
    {
        $array = [];
        
        foreach (get_object_vars($this) as $var => $value) {
            if ($value instanceof \JsonSerializable) {
                $array[$var] = $this->$var->jsonSerializeToArray();
            } else {
                $array[$var] = $this->$var;   
            }
        }
        
        return $array;
    }
}

abstract class IdOnly implements \JsonSerializable {
    use Serialize;
    
    public function __construct(public int $id) {}
}

class AcademicUnit extends IdOnly {}
class Student extends IdOnly {}

class EnrollStudentPhp8 implements \JsonSerializable
{
    use Serialize;
    
    public function __construct(
        public AcademicUnit $academicUnit,
        public Student $studentId,
        public string | null $startDate = null,
        public string | null $endDate = null,
        public bool $enrollParents = false
    ) { }
}

$enroll = new EnrollStudentPhp8(
    academicUnit: new AcademicUnit(1),
    studentId: new Student(1)
);

var_dump($enroll->jsonSerialize());

Example code of a trait that can be stacked onto any class that iterates class params and adds them to a list. I agree It is a slight perversion but for its ability to cut down on boiler plate code especially in boring models, messages etc I think forgivable.

array(5) {
  ["academicUnit"]=> array(1) {
    ["id"]=> int(1)
  }
  ["studentId"]=> array(1) {
    ["id"]=> int(1)
  }
  ["startDate"]=> NULL
  ["endDate"]=> NULL
  ["enrollParents"]=> bool(false)
}