Make sure the global namespace is always searched first.

tests/native.rs

@@ -1,4 +1,4 @@
-use rhai::{Dynamic, Engine, EvalAltResult, NativeCallContext, INT};
+use rhai::{Dynamic, Engine, EvalAltResult, ImmutableString, NativeCallContext, INT};
 use std::any::TypeId;
 
 #[cfg(not(feature = "no_module"))]
@@ -49,3 +49,41 @@ fn test_native_context_fn_name() -> Result<(), Box<EvalAltResult>> {
 
     Ok(())
 }
+
+#[test]
+fn test_native_overload() -> Result<(), Box<EvalAltResult>> {
+    let mut engine = Engine::new();
+
+    assert_eq!(
+        engine.eval::<String>(r#"let x = "hello, "; let y = "world"; x + y"#)?,
+        "hello, world"
+    );
+    assert_eq!(
+        engine.eval::<String>(r#"let x = "hello"; let y = (); x + y"#)?,
+        "hello"
+    );
+
+    // Overload the `+` operator for strings
+
+    engine
+        .register_fn(
+            "+",
+            |s1: ImmutableString, s2: ImmutableString| -> ImmutableString {
+                format!("{}***{}", s1, s2).into()
+            },
+        )
+        .register_fn("+", |s1: ImmutableString, _: ()| -> ImmutableString {
+            format!("{} Foo!", s1).into()
+        });
+
+    assert_eq!(
+        engine.eval::<String>(r#"let x = "hello"; let y = "world"; x + y"#)?,
+        "hello***world"
+    );
+    assert_eq!(
+        engine.eval::<String>(r#"let x = "hello"; let y = (); x + y"#)?,
+        "hello Foo!"
+    );
+
+    Ok(())
+}