Each protocol module has an `impl_for/1` function that returns the
implementation module or nil which works in a truthy/falsey check. So for
example:
iex(26)> String.Chars.impl_for("foo")
String.Chars.BitString
iex(27)> String.Chars.impl_for({:foo})
nil
More details here
https://hexdocs.pm/elixir/1.10.4/Protocol.html#module-reflection
-Greg Vaughn
> On Sep 26, 2020, at 5:25 PM, [email protected] <[email protected]>
> wrote:
>
> Currently we have in the stdlib Protocol.assert_impl!/2 that raises an
> exception if the given module does not implement the protocol.
>
> I think would be nice if we had a function with a similar behavior, used to
> check if the module implements a protocol, but return true or false.
>
> The use case that I have in mind, to use this function, is when serializing
> values that may be structs would be useful to just add a simple if/else to
> check if it implements a behavior like String.Chars or Enumerable.
>
> To implement this kind of functionality today I would need to try/rescue.
>
> # enumerable
> def serialize(data) when is_map(data) do
> data
> |> Enum.map(fn {key, value} -> {serialize_key(key), serialize(value)} end)
> |> Enum.into(%{})
> rescue
> Protocol.UndefinedError -> serialize_struct(value)
> end
>
> # String.Chars
> def serialize_string(%mod{} = value)
> try do
> Protocol.assert_impl!(String.Chars, mod)
> to_string(value)
> rescue
> Protocol.UndefinedError -> serialize_struct(value)
> end
> end
>
>
> Does it makes sense? Am I missing something? A predicate function to check if
> a protocol is implemented would be something acceptable in the stdlib?
>
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