Always return the same instance of a const

[adrium]

This enables:

function setAction(Action $action) {
    if ($action === Action::VIEW(); // ...
}

[mnapoli]

Hi, thank you for the proposal. I'm a bit wary to merge that because it would not solve all the problems. For example you could unserialize an enum, or simply do new MyEnum(MyEnum::FOO) (as I mentioned in #8) and get new values. So if we merge it it would be kind of an unreliable feature and it could be bad to advertise that enums are singletons.

I'd like to wait a bit to gather feedback and see if some people are interested by this and what they think of the possible downsides.

[adrium]

#44 partially solves this by making the constructor private and register the instance, if it is unserialized.

[shadowhand]

I oppose this for the reasons mentioned on #8. Enums are not entities and shouldn't be treated as singletons.

[mnapoli]

Given the comments above (and #8) let's close this for now.