diff --git a/async_simple/uthread/Async.h b/async_simple/uthread/Async.h
index 56e8fcc0b..0b8089033 100644
--- a/async_simple/uthread/Async.h
+++ b/async_simple/uthread/Async.h
@@ -41,23 +41,19 @@
 namespace async_simple {
 namespace uthread {
 
-struct Launch {
-    struct Prompt {};
-    struct Schedule {};
-    struct Current {};
+enum class Launch {
+    Prompt,
+    Schedule,
+    Current,
 };
 
-template <class T, class F,
-          typename std::enable_if<std::is_same<T, Launch::Prompt>::value,
-                                  T>::type* = nullptr>
-inline Uthread async(F&& f, Executor* ex) {
+template <Launch policy, class F>
+requires(policy == Launch::Prompt) inline Uthread async(F&& f, Executor* ex) {
     return Uthread(Attribute{ex}, std::forward<F>(f));
 }
 
-template <class T, class F,
-          typename std::enable_if<std::is_same<T, Launch::Schedule>::value,
-                                  T>::type* = nullptr>
-inline void async(F&& f, Executor* ex) {
+template <Launch policy, class F>
+requires(policy == Launch::Schedule) inline void async(F&& f, Executor* ex) {
     if (!ex)
         AS_UNLIKELY { return; }
     ex->schedule([f = std::move(f), ex]() {
@@ -67,10 +63,9 @@ inline void async(F&& f, Executor* ex) {
 }
 
 // schedule async task, set a callback
-template <class T, class F, class C,
-          typename std::enable_if<std::is_same<T, Launch::Schedule>::value,
-                                  T>::type* = nullptr>
-inline void async(F&& f, C&& c, Executor* ex) {
+template <Launch policy, class F, class C>
+requires(policy == Launch::Schedule) inline void async(F&& f, C&& c,
+                                                       Executor* ex) {
     if (!ex)
         AS_UNLIKELY { return; }
     ex->schedule([f = std::move(f), c = std::move(c), ex]() {
@@ -79,10 +74,8 @@ inline void async(F&& f, C&& c, Executor* ex) {
     });
 }
 
-template <class T, class F,
-          typename std::enable_if<std::is_same<T, Launch::Current>::value,
-                                  T>::type* = nullptr>
-inline void async(F&& f, Executor* ex) {
+template <Launch policy, class F>
+requires(policy == Launch::Current) inline void async(F&& f, Executor* ex) {
     Uthread uth(Attribute{ex}, std::forward<F>(f));
     uth.detach();
 }
diff --git a/async_simple/uthread/Collect.h b/async_simple/uthread/Collect.h
index 0edcfcf5a..e39e25132 100644
--- a/async_simple/uthread/Collect.h
+++ b/async_simple/uthread/Collect.h
@@ -50,7 +50,7 @@ namespace uthread {
 // TODO: Due to it is possible that the user of async_simple doesn't support
 // c++17, we didn't merge this two implementation by if constexpr. Merge them
 // once the codebases are ready to use c++17.
-template <class Policy, class Iterator>
+template <Launch Policy, class Iterator>
 std::vector<typename std::enable_if<
     !std::is_void<std::invoke_result_t<
         typename std::iterator_traits<Iterator>::value_type>>::value,
@@ -58,7 +58,7 @@ std::vector<typename std::enable_if<
                 type>
 collectAll(Iterator first, Iterator last, Executor* ex) {
     assert(std::distance(first, last) >= 0);
-    static_assert(!std::is_same<Launch::Prompt, Policy>::value,
+    static_assert(Policy != Launch::Prompt,
                   "collectAll not support Prompt launch policy");
 
     using ResultType = std::invoke_result_t<
@@ -93,14 +93,14 @@ collectAll(Iterator first, Iterator last, Executor* ex) {
         });
 }
 
-template <class Policy, class Iterator>
+template <Launch Policy, class Iterator>
 typename std::enable_if<
     std::is_void<std::invoke_result_t<
         typename std::iterator_traits<Iterator>::value_type>>::value,
     void>::type
 collectAll(Iterator first, Iterator last, Executor* ex) {
     assert(std::distance(first, last) >= 0);
-    static_assert(!std::is_same<Launch::Prompt, Policy>::value,
+    static_assert(Launch::Prompt != Policy,
                   "collectN not support Prompt launch policy");
 
     struct Context {