How Do I Set PHP const Variables Dynamically?

Question

I am working with an Authorize.net code sample that had a file called SampleCodeConstants.php which includes variables like so:

class SampleCodeConstants
{
    const HOME_URL = 'http://example.com';
}

This works fine if I can hard code whatever, but I am working on a Wordpress plugin so whatever needs to be set dynamically. For instance, if whatever needs to be the domain name using the plugin I will need to include Wordpress and run site_url(). To do this I added some code for setting whatever according to criteria unique to the plugin and then replaced whatever with something like $whatever.

The new code then looks something like this:

class SampleCodeConstants
{
    const HOME_URL = site_url();
}

Now instead of setting the const variables to $whatever I get:

Fatal error: Constant expression contains invalid operations

Answer 1

You can't and you shouldn't. Use a static variable instead.

class SampleCodeConstants {
    public static $HOME_URL = site_url();
}

You can then reference this as

SampleCodeConstants::$HOME_URL