PHP Class constant with php function constant giving warning

Question

I have a constants I want to return by a function like this:

public function getConst($const)
{
    $const = constant("Client::{$const}");
    return $const;
}

But this is giving me an error:

constant(): Couldn't find constant Client::QUERY_SELECT

This however, does work:

public function getConst($const)
{
    return Client::QUERY_SELECT;
}

Why not?

Aha! That's great. That works! If you give an answer I can mark it as answered. — Dion Snoeijen, Jul 13 '14 at 17:37
Nah this question is probably a duplicate anyways. Glad it worked though. — jeremy, Jul 13 '14 at 17:44
possible duplicate of [Can I get CONST's defined on a PHP class?](http://stackoverflow.com/questions/956401/can-i-get-consts-defined-on-a-php-class) — jeremy, Jul 13 '14 at 17:44

score 5 · Accepted Answer · answered Jul 13 '14 at 17:57

5

In fact this works just fine: http://3v4l.org/pkNXs

class Client {
    const QUERY_SELECT = 'foo';
}

$const = 'QUERY_SELECT';
echo constant("Client::{$const}");  // foo

The only reason this would fail is if you're in a namespace:

namespace Test;

class Client {
    const QUERY_SELECT = 'foo';
}

$const = 'QUERY_SELECT';
echo constant("Client::{$const}");  // cannot find Client::QUERY_SELECT

The reason for that is that string class names cannot be resolved against namespace resolution. You have to use the fully qualified class name:

echo constant("Test\Client::{$const}");

You may use the __NAMESPACE__ magic constant here for simplicity.

answered Jul 13 '14 at 17:57

deceze

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Yes, you are correct. I'm in a namespace. That must have been the problem. Right now I use reflection and it's working too. – Dion Snoeijen Jul 13 '14 at 18:07
But surely this is working too: return constant('Solarium\Core\Client\Client::' . $const); – Dion Snoeijen Jul 13 '14 at 18:09
Unfortunately, `__NAMESPACE__` doesn't help if I'm in another namespace than the class with the constant which I want to refer to with an alias (using `use`). – Jānis Elmeris Apr 03 '18 at 12:04
@Jānis Yeah, then you need to use the fully qualified class name. – deceze Apr 03 '18 at 12:05

score 1 · Answer 2 · answered Jul 13 '14 at 18:07

If you want to use the ReflectionClass, it would work.

$reflection = new ReflectionClass('Client');
var_dump($reflection->hasConstant($const));

More verbose example, it might be over kill ( not tested )

public function getConst($const)
{
   $reflection = new ReflectionClass(get_class($this));
   if($reflection->hasConstant($const)) {
     return (new ReflectionObject($reflection->getName()))->getConstant($const);
   }
}

PHP Class constant with php function constant giving warning

2 Answers2