On 24.05.2009, at 07:01, Feng wrote: > clojure.contrib.types/deftype assumes data to tag are created fresh > with no meta data. Would it be useful to have it update meta data if > data are already initialized with meta data, e.g. from file or db with > other meta data, but :type ::constructor are too program specific to > be stored in there?
I considered this, but decided to postpone any action until the problem actually occurs. The reason why I prefer the current approach wherever it is applicable (i.e. for any values that don't need metadata other than for type identification is the associated overhead. My current implementation creates a single metadata map per type that is then attached to each data item. The memory overhead is negligible, and the CPU time overhead is just one call to with-meta per object creation. The modification that you propose (as well as the variant I had considered, using vary-meta) creates a metadata map per object, resulting in potentially lots of metadata maps, even though many could be identical, and requiring map operations of non- negligible cost for each object creation. Several solutions are envisageble: 1) Check if the object has metadata, and put on a predefined map if not. This leads to an increased CPU overhead for each object creation, to to a memory overhead only for types that actually require it. 2) Make the metadata handling an option specified by a parameter to deftype. 3) Delegate metadata handling to the constructor, at least optionally. It's hard to choose among these solutions without having some real- life use cases. Konrad. --~--~---------~--~----~------------~-------~--~----~ 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 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 -~----------~----~----~----~------~----~------~--~---
