(test) added bench code for large each loop [#166]

Signed-off-by: Ning Sun <sunng@about.me>

benches/bench.rs

@@ -2,6 +2,9 @@
 extern crate handlebars;
 extern crate serde;
 extern crate serde_json;
+#[macro_use]
+extern crate serde_derive;
+
 extern crate test;
 
 use std::collections::BTreeMap;
@@ -66,3 +69,23 @@ fn render_template(b: &mut test::Bencher) {
     let data = make_data();
     b.iter(|| handlebars.render("table", &data).ok().unwrap())
 }
+
+#[derive(Serialize)]
+struct DataWrapper {
+    v: String,
+}
+
+#[bench]
+fn large_loop_helper(b: &mut test::Bencher) {
+    let mut handlebars = Handlebars::new();
+    handlebars
+        .register_template_string("test", "BEFORE\n{{#each me}}{{this.v}}{{/each}}AFTER")
+        .ok()
+        .expect("Invalid template format");
+
+    let data: Vec<DataWrapper> = (1..10000)
+        .into_iter()
+        .map(|i| DataWrapper { v: format!("n={}", i) })
+        .collect();
+    b.iter(|| handlebars.render("test", &data).ok().unwrap());
+}