(def v) with no init supplied destroys #'v metadata
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Sean Corfield January 10, 2018 at 1:33 AM
If Stuart is right that this is considered the correct behavior for def then defonce should not use (def ~name) – per CLJ-1148. Could we get a decision once and for all and then reject this issue if the behavior is as designed? Or do we want a patch to update the docstring to make the metadata issue clear?
Andy Fingerhut July 31, 2015 at 9:00 PM
CLJ-1213 might be related, but it doesn't mention metadata, only (def foo) without init value given.
Stuart Halloway July 31, 2015 at 8:49 PM
I am pretty sure we have been here before, and decided that def is working as desired. (If anybody can find the thread/ticket please add a link.) I think this should be a doc enhancement.
If the behavior of defmethod is a separate bug, please make a separate ticket for that, showing an example problem.
nahuel June 14, 2014 at 1:35 AM
Alex Miller: It seems CLJ-1148 is an special case where this problem shows, but the patches in CLJ-1148 only fixes the issues for defonce, not generally for def, not for defmulti and not clarifies this behaviour in the def special form documentation.
Alex Miller June 13, 2014 at 10:14 PM
I think this is mostly a dupe of CLJ-1148 but I'll leave it as it states the specific problem more precisely.
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(def a) destroys #'a metadata, check this:
If this is not a bug but a "feature", then we have at least two problems:
1- The def special form documentation doesn't state this behaviour at all, it needs to be clarified. With the current documentation it seems as doing a def with no init supplied will not make any side-effect at all, and this is not true for the var metadata.
2- defmulti uses this form to lookup the var and check if it already binds to a MultiFn, if that is the case then defmulti does nothing... but it really does something, defmulti will destroy the original var metadata in the (supposedly non-destructive) check. This is the involved defmulti fragment: