I think there are differences here due to the two mechanisms for treating a
Var as dynamic. This reminds me of the
ticket http://dev.clojure.org/jira/browse/CLJ-859 as well. I'm not sure
what the proper resolution should be as there are several ways to go with
it.
On Saturday, July 30, 2016 at 3:20:16 PM UTC-5, Yuri Steinschreiber wrote:
>
> Hello -
>
> The documentation specifies that 'def' and 'intern' have the same behavior
> with regards to metadata on the Var they define/intern. So I expected these
> to be equivalent:
>
> (def ^:dynamic my-var)
>
> (intern *ns* (with-meta 'my-var {:dynamic true}))
>
> Indeed, (meta #'my-var) correctly show :dynamic true in either case.
>
> However,
>
> (binding [my-var :foo] my-var)
>
> throws an exception in the case of intern usage, complaining that the Var
> is non-dynamic.
>
> The analysis of Clojure source reveals that
> clojure.lang.Var/pushThreadBindings checks a member isDynamic, rather than
> the metada itself. Which is understandable from the performance point of
> view. Problem is the Var's property isDynamic is set by 'def' special form
> only, while 'intern' doesn't do it.
>
> Am I correct in thinking that either the doc needs to be updated to
> reflect a special status of 'def' in regard to dynamic Vars, or 'intern'
> has a bug?
>
> I personally think its a bug in 'intern'. It can be circumvented by using
> Java interop on the Var, like (.setDynamic #'my-var) after interning it,
> but it looks ugly.
>
> The reason I stumbled on it is I need to intern a dynamic Var in a macro,
> and using 'def' in a macro doesn't seem to quite work with metadata - it's
> apparently being processed by the reader at a wrong time (maybe I'm missing
> something, but that's a question for another day.) I tried to use 'intern'
> instead and hit the problem described above.
>
> Cheers.........................Yuri
>
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