It's fairly common in situations like this to use a namespaced keyword. For instance ::unknown (which is short for my.namespace/unknown).
On Mon, Jan 14, 2013 at 6:06 PM, Frank Siebenlist < frank.siebenl...@gmail.com> wrote: > I'm using those watcher-fns that get called when the watched ref changes, > and the watcher-fn gets passed the old-value and the new-value. > > Now, nil is a proper value for a key-value and well as a val-value in a > map, so passing nil does not give you the info whether or not an old-value > existed or not, or whether a new-value is nil or no-value. > > With the getter fn: (get m k no-value-here), you have the option to pass > this no-value-here argument which gets returned if there was no value - > this allows you to distinguish nil from "no-value". However, in the > watcher-fn you cannot pass such a no-value argument. > > One possible solution would be to define a well-know URI for the value of > "no-value" - something like for example: "uri: > http://clojure.org/uri/no-value";, or some other standardized constant. > > Any other/better suggestions? > > Thanks, FrankS. > > -- > 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 > -- “One of the main causes of the fall of the Roman Empire was that–lacking zero–they had no way to indicate successful termination of their C programs.” (Robert Firth) -- 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
