I want to be able to look up the value of a constant dynamically, but using a variable doesn't work with the syntax.
<?php
class Food {
const FRUITS = 'apple, banana, orange';
const VEGETABLES = 'spinach, carrot, celery';
}
$type = 'FRUITS';
echo Food::FRUITS;
echo Food::$type;
?>
gives
apple, banana, orange
Fatal error: Access to undeclared static property: Food::$type
How can I dynamically call the constant?
The only solution which comes to my head is using a constant function:
echo constant('Food::' . $type);
Here you create name of a constant, including class, as a string and pass this string ('Food::FRUITS') to constant function.
This will be available natively in php8.3 as of November 2023
class MyClass {
public const MY_CONST = 42;
}
$constName = 'MY_CONST';
echo MyClass::{$constName};
https://php.watch/versions/8.3/dynamic-class-const-enum-member-syntax-support
A ReflectionClass can be used to get an array of all of the constants, and then the value of the specific constant can be found from there:
<?php
class Food {
const FRUITS = 'apple, banana, orange';
const VEGETABLES = 'spinach, carrot, celery';
}
$type = 'FRUITS';
$refClass = new ReflectionClass('Food');
$constants = $refClass->getConstants();
echo $constants[$type];
?>
When using namespaces, make sure you include the namespace, even if it's autoloaded.
namespace YourNamespace;
class YourClass {
public const HELLO = 'WORLD';
}
$yourConstant = 'HELLO';
// Not working
// >> PHP Warning: constant(): Couldn't find constant YourClass::HELLO ..
constant('YourClass::' . $yourConstant);
// Working
constant('YourNamespace\YourClass::' . $yourConstant);```
you can create associative array
class Constants{
const Food = [
"FRUITS " => 'apple, banana, orange',
"VEGETABLES" => 'spinach, carrot, celery'
];
}
and access value like this
$type = "FRUITS";
echo Constants::Food[$type];
