Comment by nightpool

    [Speculative optimizations] may not suffice in this case as future planned optimizations may wish to rely not only on immutability within the lifetime of the process, but also on the immutability of fields from one run of the application to the next.

Can someone elaborate a little more on what this means? I'm very surprised to hear that this was considered a blocker important enough to add all of this complicated machinery (and breaking several deserialization libraries...), when I've never even heard of such an optimization and can't imagine what sort of form it would take