Expand packages and raw Engine write-up.

tests/packages.rs

@@ -0,0 +1,33 @@
+use rhai::{Engine, EvalAltResult, INT, Scope};
+use rhai::packages::{Package, StandardPackage};
+
+#[test]
+fn test_packages() -> Result<(), Box<EvalAltResult>> {
+    let e = Engine::new();
+    let ast = e.compile("x")?;
+    let std_pkg = StandardPackage::new();
+
+    let make_call = |x: INT| -> Result<INT, Box<EvalAltResult>> {
+        // Create a raw Engine - extremely cheap.
+        let mut engine = Engine::new_raw();
+
+        // Load packages - cheap.
+        engine.load_package(std_pkg.get());
+
+        // Create custom scope - cheap.
+        let mut scope = Scope::new();
+
+        // Push variable into scope - relatively cheap.
+        scope.push("x", x);
+
+        // Evaluate script.
+        engine.eval_ast_with_scope::<INT>(&mut scope, &ast)
+    };
+
+    // The following loop creates 10,000 Engine instances!
+    for x in 0..10_000 {
+        assert_eq!(make_call(x)?, x);
+    }
+
+    Ok(())
+}