ref & out parameters are not handled yet. This is one of four CLR interop problems waiting for solutions. See the CLR Interop page on the wiki for the others.
Three of the four, including this one, have fairly simple solutions at the interop interface, but require some extension to Clojure to create a good solution for the Clojure programmer. Hence, input from Clojurians and ultimately a blessing from the chief are requested/ required. For ref & out parameters, the problem is that let bindings and fn parameters are not variables. You can't change the values they are bound to. ref and out change the values bound to the variables passed as parameters. So if we implement ref/out silently, (let [ a nil ] ... (DateTime.TryParse "2009/10/20" a) ... ) where subsequent to the call the value bound to a has changed, then we've just changed Clojure semantics non-trivially. Anything that introduces (let, fn) or changes (recur) a local name/ value binding at the moment is a special form, or a macro that ultimately expands to a special form. Do we need something equivalent here? I don't have enough use cases to make a design decision here. Suggestions welcome. On Nov 2, 1:38 am, Miron Brezuleanu <mbr...@gmail.com> wrote: > Hello, > > One question about CLR interop: what is the correct way to handle > 'out' parameters in Clojure code? The following doesn't work: > > Clojure 1.1.0-alpha-SNAPSHOT > user=> (def a (DateTime.)) > #'user/a > user=> (DateTime/TryParse "2009/10/20" a) > True > user=> a > 1/1/0001 12:00:00 AM > user=> > > I guess TryParse creates another instance of a DateTime, and the > instance passed via 'a' is left unmodified. > > I believe the same problem applies to 'ref' parameters. > > Thanks, > -- > Miron Brezuleanu --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
