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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