weird php implementation for default value - php

Question

I am working on an OOP implementation and I have the following:
abstract class Parent{
public abstract function select($order="desc");
}
class Child extends Parent{
public function select($order) // here is the problem error
{
// selection code
}
}
This throws an error that tells me the declaration must be compatible with the parent method.
I did implement it with the right parameters except I didn't carry over the default parameter setting.
I do not want to copy past the same prototype of parent method in 100 classes if i want someday change the default value. How can I do this?
does generic exist in php ??

Answer 1

public abstract function select($order="desc");
and public function select($order) dont match.
remove the default value from the abstract function.

Answer 2

About the only way I can see to avoid updating a lot of values if you ever want to change the common default is this:
abstract class Parent{
const DEFAULT_SELECT_ORDER = "desc";
public abstract function select($order = "");
protected static function select_order(&$order)
{
if (empty($order) || !in_array(strtolower($order), array("asc", "desc"))) {
// additional test to check if the value is valid
$order = self::DEFAULT_SELECT_ORDER;
}
}
}
class Child extends Parent{
public function select($order = "") // here is the problem error
{
self::select_order($order);
// selection code
}
}
Hmm - another, probably better approach:
abstract class Parent {
protected $order = "desc";
public function order($order) {
if (in_array(strtolower($order), array("asc", "desc"))) {
$this->order = $order;
} else {
// probably should throw an exception or return false or something
}
return true;
}
public abstract function select();
}
class Child extends Parent {
public function select() {
// select code using $this->order
}
}
$query = new Child();
$query->order("asc");
$results = $query->select();

Answer 3

All you need to do is change your extended method to be something like:
public function select($order="some other value") // here is the problem error
{
// selection code
}
Essentially because the original method has a default value then ALL overrides must have a default value.
In order to do what you want you would have to make $order an object property of Parent and change the method signature to get rid of the $order parameter. Then within any specific implementation you could simply set $order to whatever else you want.

Answer 4

You possible could use my tiny library ValueResolver, for example:
$myVar = ValueResolver::resolve($var, $default);
and don't forget to use namespace use LapaLabs\ValueResolver\Resolver\ValueResolver;
There are also ability to typecasting, for example if your variable's value should be integer, so use this:
$id = ValueResolver::toInteger('6 apples', 1); // returns 6
$id = ValueResolver::toInteger('There are no apples', 1); // returns 1 (used default value)
Check the docs for more examples