Elixir with Erlang fun2ms -> ETS

Questions & Help Questions
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1

Hi, does anyone know how I can create a matchspec for this condition?

matchspec = :ets.fun2ms(fn({key, test}) when key != :counter -> test end)

[error] exited in: :ets.fun2ms(:function, :called, :with, :real, :fun, :should, :be, :transformed, :with, :parse_transform, :or, :called, :with, :a, :fun, :generated, :in, :the, :shell)
        ** (EXIT) :badarg

I can get the result I want with:

test = :ets.foldl(fn({key, obj}, acc) -> case key != :counter do
                                           true -> [obj | acc]
                                           _ -> acc
                                         end
 end, [], :queue_cache)

or

 test = :ets.foldl(fn({key, obj}, acc) when key != :counter -> [obj | acc]
                   (_, acc) -> acc
 end, [], :queue_cache)

But fun2ms seems a bit cleaner to write - I’m not sure I understand the restraints in fun2ms, perhaps is my when condition that’s not valid?