On Sunday, 1 March 2015 at 20:39:54 UTC, Michel Fortin wrote:
There's a problem with reference counting immutable objects: they are implicitly shared. Any metadata attached to them thus needs to be shared. Accessing the metadata through a global shared hash table isn't going to be that much of a performance hit compared to whatever mechanism is used to synchronize access to that data.
But there is no difference between having metadata as part of the object and using a hash table as long as the mutable and immutable data sits on separate cache lines. (The object address is basically a hash key, and memory is a big table).
