How can I make my class variable assignment dynamic? - php

Question

In the following code, I want to assign an $settings's key, help to a constant class variable value, $To_default. However, I am told Constant expression contains invalid operations. Is there any way I can get around this?
class EmailClass extends PluginBase {
private $To_default = 'scrollout#stackoverflow.com';
protected $settings = array(
'To'=>array(
'type'=>'text',
'label'=>'To',
'help'=>$this->To_default, // Constant expression contains invalid operations
),
);
I've tried declaring $To_default in various ways including private const $To_default, static private $To_default, etc. but none worked. $settings is not static, as you can see, so I don't understand why this is a problem.

Answer 1

Don't know deep technical explanation for this but I think this is because normally you initialize properties in the constructor, like so:
class EmailClass
{
private $To_default = 'scrollout#stackoverflow.com'; // not a constant, so better throw it into constructor too
protected $settings;
public function __construct() {
$this->settings = array(
'To'=>array(
'type'=>'text',
'label'=>'To',
'help'=>$this->To_default
)
);
}
}
Analogical I don't know why: 'if isset(expression)' doesn't work but it doesn't have to. There's a better solution: 'if(expression)'. This is just how we do it.

Answer 2

You can not specify a default value that refers to another class property ($settings is an array that tries to read $To_default).
My recommendation is that $settings can be the result of a getter method, for example getSettings, and inside of it you can build an array and return it.
By doing do this, you can also decide to override the $To_default value with a setTo method.
Here is an example:
<?php
class EmailClass extends PluginBase {
private string $toDefault = '';
/**
* #param string $toDefault
*/
public function __construct( string $toDefault = 'scrollout#stackoverflow.com' ) {
$this->toDefault = $toDefault;
}
/**
* #param string $toDefault
*/
public function setToDefault( string $toDefault ): void
{
$this->toDefault = $toDefault;
}
public function getSettings(): array
{
return [
'TO' => [
'type' => 'text',
'label' => 'To',
'help' => $this->toDefault,
]
];
}
}

Answer 3

Use a class constant rather than a variable for the default.
Constants don't begin with $, that's the problem you had when you tried this.
class EmailClass extends PluginBase {
private const TO_DEFAULT = 'scrollout#stackoverflow.com';
protected $settings = array(
'To'=>array(
'type'=>'text',
'label'=>'To',
'help'=>self::TO_DEFAULT, // Constant expression contains invalid operations
),
);
}