Consider adding an accessor to query the initialization state of a lazy static

[Kimundi]

Similar to lazy_static::initialize() there could be a lazy_static::is_initialized().

This could be used to give code that might run into a initialization cycle issue an way to avoid it.

However, it seems that std::sync::Once does not support this.

[tmccombs]

I looked into this a little, and the lack of support in std::sync::Once isn't that much of a problem, because we can just check if the stored pointer is non-null. A bigger problem is that LAZY is defined inside of the deref method implementation, so it isn't accessible by an is_initalized function. I don't know of a way to move the declaration of LAZY out of the method in stable rust with any kind of namespace.

[Kimundi]

The issue with checking against 0 or None is that we could be racing against a concurrent initialisation of the static, while going through the Once API itself would presumably correctly synchronize the access.

[Pauan]

There is a Nightly-only API for checking whether a Once is initialized or not.

However, I think an even better option is to use parking_lot's implementation of Once, which has an even better API which works on Stable.