The points about encapsulation are pointed at immutable fields (which are public) and don't hold for mutable fields, which are provided as an advanced mechanism for building higher-level constructs.
The deftype docstring says: Fields can be qualified with the metadata :volatile-mutable true or :unsynchronized-mutable true, at which point (set! afield aval) will be supported in method bodies. Note well that mutable fields are extremely difficult to use correctly, and are present only to facilitate the building of higher level constructs, such as Clojure's reference types, in Clojure itself. They are for experts only - if the semantics and implications of :volatile-mutable or :unsynchronized-mutable are not immediately apparent to you, you should not be using them. As the datatypes reference page also says, "Concrete derivation is bad" - this is not something we have any desire to enable or support. Some other options that usually are better: - Define interfaces and have the deftype implement them for access - Use composition instead of inheritance - Use fields holding Clojure stateful constructs (like atoms) On Monday, August 27, 2018 at 1:08:21 AM UTC-5, Didier wrote: > > It seems to contradict the documentation found here datatypes > <https://clojure.org/reference/datatypes#_deftype_and_defrecord>: > > > Encapsulation of information is folly. Fields are public, use > protocols/interfaces to avoid dependencies > > It is also not documented in the doc-string, and makes it impossible to > further extend the type. No more ad-hoc polymorphism basically. > > So you can't do this: > > (deftype MutableBox [^{:volatile-mutable true} contents]) > > (defprotocol Container > (inventory [this])) > > (extend-type MutableBox > Container > (inventory [this] (.-contents this))) > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
