diff --git a/demo/cpp/demo.cc b/demo/cpp/demo.cc
index 25a6109..84aef41 100644
--- a/demo/cpp/demo.cc
+++ b/demo/cpp/demo.cc
@@ -2,11 +2,12 @@
 #include <functional>
 #include "tiny_pool.h"
 
-class TinyPool {
+class TinyPool { // OOP for tiny_thread_pool
     pool_t *pool;
-    static void wrap_c_func(void *func) {
-        (*static_cast<std::function<void()>*>(func))();
-        free(func);
+    static void wrap_c_func(void *func) { // wrap std::function as c-style function ptr
+        auto func_ptr = static_cast<std::function<void()>*>(func);
+        (*func_ptr)();
+        delete func_ptr; // free lambda function
     }
 
 public:
@@ -17,25 +18,22 @@ public:
     explicit TinyPool(uint32_t size) { pool = tiny_pool_create(size); }
 
     template <typename Func, typename ...Args>
-    auto submit(Func &&func, Args &&...args) -> std::future<decltype(func(args...))>;
+    auto submit(Func &&func, Args &&...args) -> std::future<decltype(func(args...))> { // submit new task
+        std::function<decltype(func(args...))()> wrap_func = std::bind(
+            std::forward<Func>(func), std::forward<Args>(args)... // wrap as a function without params
+        );
+        auto func_ptr = std::make_shared<
+            std::packaged_task<decltype(func(args...))()> // function task as shared ptr
+        >(wrap_func);
+        tiny_pool_submit(pool, TinyPool::wrap_c_func, (void*)( // submit with thread pool interface
+            new std::function<void()> (
+                [func_ptr]() { (*func_ptr)(); } // create lambda for running task
+            )
+        ));
+        return func_ptr->get_future(); // return future object
+    }
 };
 
-template <typename Func, typename ...Args>
-auto TinyPool::submit(Func &&func, Args &&...args) -> std::future<decltype(func(args...))> {
-    std::function<decltype(func(args...))()> wrap_func = std::bind(
-        std::forward<Func>(func), std::forward<Args>(args)...
-    );
-    auto func_ptr = std::make_shared<
-        std::packaged_task<decltype(func(args...))()>
-    >(wrap_func);
-    tiny_pool_submit(pool, TinyPool::wrap_c_func, (void*)(
-        new std::function<void()> (
-            [func_ptr]() { (*func_ptr)(); }
-        )
-    ));
-    return func_ptr->get_future();
-}
-
 /// ------------------------------------ start test ------------------------------------
 
 #include <iostream>