Add comments and in_env variant returning a ref again

rustler/src/types/reference.rs

@@ -4,9 +4,20 @@ use crate::{Decoder, Encoder, Env, Error, NifResult, Term};
 
 use crate::sys::enif_make_ref;
 
+/// Wrapper for BEAM reference terms.
 #[derive(PartialEq, Eq, Clone, Copy)]
 pub struct Reference<'a>(Term<'a>);
 
+impl<'a> Reference<'a> {
+    /// Returns a representation of self in the given Env.
+    ///
+    /// If the term is already is in the provided env, it will be directly returned. Otherwise
+    /// the term will be copied over.
+    pub fn in_env<'b>(&self, env: Env<'b>) -> Reference<'b> {
+        Reference(self.0.in_env(env))
+    }
+}
+
 impl<'a> Deref for Reference<'a> {
     type Target = Term<'a>;
 
@@ -46,6 +57,7 @@ impl<'a> Encoder for Reference<'a> {
 }
 
 impl<'a> Env<'a> {
+    /// Create a new reference in this environment
     pub fn make_ref(self) -> Reference<'a> {
         unsafe { Reference(Term::new(self, enif_make_ref(self.as_c_arg()))) }
     }