Make $_ENV usable in attributes

[Valentinfe]

Description

In my opinion, attributes usage is expanding and adding variables handling or at least $_ENV handling could prove very useful.

#[AsCronTask(expression: '0 */1 * * *', schedule: 'status_updater')]
public class Task{}

As you can see in this exemple, I would love to put this expression in an env var but I think it's not doable right now.

#[AsCronTask(expression: $_ENV['TASK_FREQUENCE'], schedule: 'status_updater')]
public class Task{}

Can you maybe give an explanation on why this is not doable. And if it is doable could it be added ?

[iluuu1994]

This is not currently allowed because variables are not available from constant expressions. Constant expressions originally always evaluated to the same value. This isn't really the case anymore since https://wiki.php.net/rfc/new_in_initializers. I suppose we could make an exception for $_ENV (or getenv()). That said, constant expressions can be cached, in which case changes to the environment won't actually be reflected by new instances of the attribute. So, whether it is a good idea, I don't know. You could instead store the env-value in a constant and then pass that to the attribute.

[iluuu1994]

To clarify: https://3v4l.org/1au9I Not particularly pretty, but this should achieve what you're asking for.

[Valentinfe]

Thank you ! Your answer is clear and solved our problem.

[Valentinfe]

I don't know if this issue needs to be closed or if this could lead to an evolution, I will let your team conclude on that.

[iluuu1994]

@Valentinfe I would say, lets. This RFC is unlikely to happen if someone doesn't push it forward, and even then it's not particularly likely (I believe) to be accepted.