clojure structs are an optimized version of maps for a set of shared keys. if you don't have a defined set of shared keys you just have a map. so by all means, use a map
On Tue, Jan 19, 2010 at 3:52 PM, Andreas Wenger <andi.xeno...@googlemail.com> wrote: > Hi, > > I would like to know why defstruct without providing any keys (like > "(defstruct s)") is not allowed (exception: "Must supply keys"). > > Let me shortly describe why I think that this would be useful: Imagine > you have a defstruct like in Rich's Ants demo: > > (defstruct cell :food :pher) ;may also have :ant and :home > > :ant and :home are optional, since they are not often used (Rich > actually states in his talk, that this is an advantage compared to > Java where we would always have to store "null" for each of the > optional class members). Image, you use (struct-map cell ...) very > often in your program. Now, you notice that :food and :pher are also > not used very often, and that most times only one or two of the four > possible keys are actually used. So you make them all optional: > > (defstruct cell) ;may have :food, :pher, :ant and :home > > This is not allowed. You have to remove the whole defstruct, which > makes all your (struct-map cell ...) calls useless. This is bad, > because you have to replace it everywhere and struct-map has a very > nice documentary style you want to use anyway. (Later, when we notice > that at least one key is obligatory, we again have to find these > places and convert them back to struct-map...) > > In practice, I had this problem with a struct containing 10 possible > keys, where mostly only 1-2 are used in practice. Now I have to remove > the whole defstruct... or let at least one arbitrary key be non- > optional, which is more a hack than a nice solution. > > Looking in the PersistentStructMap.java, I found out that allowing > structs with no obligatory key would be no problem at all (change 2 > lines?). I don't know why it was written that way, but I think here > Clojure puts a spoke in me wheel where it just not needed. > > Any comments? Thanks! > > > Andi > > -- > 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 > -- And what is good, Phaedrus, And what is not good— Need we ask anyone to tell us these things?
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