impl Serialize for OnceCell

[tamuhey]

Like RefCell, it is useful if OnceCell can be serialized with serde.

[Nohac]

I see the PR was closed due to lack of real-world use cases, so I wanted share how I would use it.

I'm currently working on a DSL where I first produce an AST, I then do some validation, as well as adding type information to each node in the AST. Adding the type information only happens once, but it requires that the full AST exists first.

To me, OnceCell seems to be the perfect candidate for this type of lazy/late initialization, as it doesn't require mutable access, and returns Option<&T> instead of Ref<'_, T> (which I find to be very annoying to work with).
It's the perfect alternative to RefCell<Option<T>> (or other mutable types) where the value only needs to be initiated once, it is also the least verbose.

The reason I need the AST to be serializable is so I can use it for code generation from different languages like typescript etc. later on.

I understand that this probably won't make you reconsider. I'm also evaluating alternatives to the way I'm currently doing things, but having support for OnceCell would make things a bit simpler.

Edit: The same goes for OnceLock

[jayvdb]

fwiw, I am haphazardly maintaining https://crates.io/crates/once_cell_serde