pub fn derive_prefer_externalptr(input: DeriveInput) -> Result<TokenStream>Expand description
Derive PreferExternalPtr: adds the PrefersExternalPtr marker trait and an
IntoR impl that wraps the value in ExternalPtr::new before converting to SEXP.
The type must implement TypedExternal (typically via #[derive(ExternalPtr)]).
The generated IntoR::Error is Infallible.