mcjordalini mcjordalini - 1 year ago 88
PHP Question

PHP, OOP: Why can't the array property of my class use properties & methods as values like an array outside of a class can?

So like the title says, I am having a hard time making an array property of one of my classes have it's values be declared as properties & methods.

I can successfully do this if the array is not a property of a class, but as soon as the array is dropped into a class, the script doesn't like those values, and throws me this error.

Fatal error: Constant expression contains invalid operations in C:\xampp\htdocs_webdev\repos\mcf\static\inc\classes\class.catalogue.php on line 17

I have both classes being included in a different
. That file is then included in each page. Here is some code to better illustrate my issue,

Master Class File:

// config
require_once('config/config.php'); // config file

// other tools
require_once(ROOT_DIR . 'inc/parsedown/Parsedown.php'); // tool that I am using for parsing .md files

// my classes
require_once(ROOT_DIR . 'inc/classes/class.vendor.php');
require_once(ROOT_DIR . 'inc/classes/class.catalogue.php');

Class A:

class Vendor
public $vendor = array(
'foo' => array(
'name' => 'Foo Inc.',
'image' => (VENDOR_IMG . 'foo/foo-logo.png'),
'bar' => array(
'name' => 'Bar Co.',
'image' => (VENDOR_IMG . 'bar/bar-logo.png'),

public function get($data) {
if (array_key_exists($data, $this->vendors)) {
return $this->vendors[$data];
} else {
// throw error

// Class methods...

Class B:

class Catalogue
public $catalogue = array(
'1' => array(
$section = $markdown->text(file_get_contents(ROOT_DIR . catalogue/markdown/')),
$link = 'catalogue/pdf/section1.pdf,
$pdf = (ROOT_DIR . $link),
'title' => 'Section One',
'content' => mdReplace($section, $pdf, $link),
'theme' => 'purple',
'vendors' => array(
1 => $vendor->get('foo'),
2 => $vendor->get('bar'),
// '2' ...

// Class methods...

is a small function located in a seperate php file called
. It's purpose is to replace a few keywords inside of the
files that contain the sections' content.)

Apologies in advance if I am just blind as a bat right now and am missing something obvious.

Answer Source

If you read php oop manual carefully, here what you will see:

Class member variables are called "properties"... They are defined by using one of the keywords public, protected, or private, followed by a normal variable declaration. This declaration may include an initialization, but this initialization must be a constant value--that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated.

See the words

must not depend on run-time information

And your current definition of public $catalogue is dependant of some data that will be evaluated later. That's why you have fatal error.

So, as said the solution is to fill $catalogue data by calling some function - either explicitly or in a __construct for example.

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