Does this mean that it will not capture dynamics/composed queries?
trechubet
msimonborg
The simpler way to do this now is defguard is_query(a) when is_struct(a, Ecto.Query) using Kernel.is_struct/2, which was introduced after this thread was last active. PR #9470
As for your question, I am not 100% sure, but if what you have created is an Ecto.Query struct, it will match
3
dimitarvp
wojtekmach
Hex Core Team
It is impossible to do in a defguard. I think it is possible, with big caveats so maybe actually impossible too, with a defmacro. If the protocol is consolidated, you can grab the list of modules implementing it. So if your protocol is consolidated by the time you call your guard, which generally may not necessarily be the case, that should work. Here’s a sketch:
defmodule Macros do
defmacro is_impl(term, protocol) do
protocol = Macro.expand(protocol, __ENV__)
impls =
case protocol.__protocol__(:impls) do
{:consolidated, impls} ->
impls
:not_consolidated ->
raise "#{inspect(protocol)} is not consolidated"
end
quote do
unquote(term).__struct__ in unquote(impls)
end
end
end
defmodule Foo do
import Macros
def f(enumerable) when is_impl(enumerable, Enumerable) do
Enum.to_list(enumerable)
end
end
besides the caveat around consolidation time, in the list of impls we have things like Atom, Integer, …, Any, and they all would have to be handled too.
So yeah, not worth it. 
1