How can I set default values in the constructor of an abstract class?

Question

I have an abstract class that contains the __construct method like this

abstract class Model
{
    protected $attributes = [];

    public function __construct(array $attributes = []) {
        $this->$attributes = $attributes;
    }
}

Then in my concrete class I extend the abstract Model

class Pong extends Model
{
    
}

When I dump the attributes inside the constructor I get an empty array, but if I remove the default value of the constructor parameter, the Pong model has attributes. The challenge is, I want to be able to construct the concrete class both with default values and without

$pong = new Pong();
$pong = new Pong(['msg' => 'Hello Kitty']);

`$this->$attributes` should be `$this->attributes`. https://3v4l.org/u6lm2 — Phil, Jul 13 '20 at 07:08
Your code actually throws an array-to-string conversion error. I suggest you improve your error reporting configuration. See [How can I get useful error messages in PHP?](https://stackoverflow.com/questions/845021/how-can-i-get-useful-error-messages-in-php) — Phil, Jul 13 '20 at 07:15
Thanks, yeah a stupid typo, I've been starring at it for too long — kristian nissen, Jul 13 '20 at 07:18

era-net · Accepted Answer · 2020-07-13T07:20:53.933

-1

Give this a try:

I made the $attributes public, to show the results.

Note the question marks ??.

<?php

class Model
{
    public $attributes = [];

    public function __construct(array $attr = []) {
        $this->attributes['msg'] = $attr['msg'] ?? "default";
        $this->attributes['someValue'] = $attr['someValue'] ?? 'default';
    }
}

class Pong extends Model
{
    
}

$pong = new Pong();
print_r($pong->attributes);

Play around with the code you see above!

edited Jul 13 '20 at 07:20

answered Jul 13 '20 at 07:17

era-net

387
1
11

Nice with the ?? didn't know I could do that – kristian nissen Jul 13 '20 at 07:19

How can I set default values in the constructor of an abstract class?

1 Answers1

Give this a try: