How do I iterate through a child's private fields? - php

Question

After reading this question
One idea for my problem was to implement the method in the child classes like:
class Child {
private $childField = "Want to see";
public $pubChildField = "Will see";
public function method()
{
$assoc = []; // a associative array
foreach ($this as $field => $value) {
$assoc[$field] = doStuff($value);
}
return $assoc;
}
}
var_dump((new Child())->jsonSerialize());
But for this I'd have to copycat the code in each child class. For readability, I want to refactor it into an (already existing) parentClass similar to:
abstract class parentClass {
public function method()
{
$assoc = []; // a associative array
foreach ($this as $field => $value) {
$assoc[$field] = doStuff($value);
}
return $assoc;
}
}
class Child extends parentClass {
private $childField;
public $pubChildField;
}
var_dump((new Child())->jsonSerialize());
Both foreach ($this as $k=>$v) and get_object_vars() will get the public fields from the instance. I need to get it's private fields thou, for serialization.
Edit 1: Typo abstract method - what was i thinking
Edit 2: Clarified the example
Edit 3: Reformulated the question since there seemed to be misconception

Answer 1

Abstract class is about abstract methods, not inherited. I assume these
are not relevant to the problem (otherwise make it ordinary default/base class).
private limits visibility to concrete class - use protected
instead.
It seems to me that you need only code reuse. You might reach for traits in this casse - traits becoming part of a class, and you can iterate private fields.
interface ArrayData {
public function toArray(): array;
}
trait ToArray {
public function toArray(): array {
$assoc = []; // a associative array
foreach ($this as $field => $value) {
$assoc[$field] = $value;
}
return $assoc;
}
}
class Foo implements ArrayData {
use ToArray;
private $childField = "Want to see";
public $pubChildField = "Will see";
}
$foo = new Foo();
var_dump($foo->toArray());

Answer 2

The correct solution is to declare the base class implements the JsonSerializable interface and implement the JsonSerializable::jsonSerialize() method in all children classes.
You can let it unimplemented in the base class to force all the children classes implement it or you can provide a default implementation (return array();) in the base class for the children classes that do not need to be serialized.
The implementation in each class should not iterate over the list of object properties. Usually, not all object properties must be serialized and the serializable properties are not born equal.
abstract class parentClass implements JsonSerializable {
// You can remove this default implementation
// to force all children class implement the method
public function jsonSerialize()
{
return array();
}
}
class childClass extends parentClass {
private $childField;
public $pubChildField;
public function jsonSerialize()
{
return array(
'field1' => $this->childField,
'field2' => base64_encode($pubChildField),
// etc ...
);
}
}
var_dump((new Child())->jsonSerialize());
Try to write code that is easier to read and understand. You will thank yourself later.