More direct overload resolution control in folly::coro::concat

Summary: [Folly] More direct overload resolution control in `folly::coro::concat`. Just name the type directly rather than using SFINAE, when the SFINAE would just name the type directly in a more roundabout way. Differential Revision: D18746633 fbshipit-source-id: 6da909834b511426b1cf7bbda0fd7643b5761f14

More direct overload resolution control in folly::coro::concat
Summary: [Folly] More direct overload resolution control in `folly::coro::concat`. Just name the type directly rather than using SFINAE, when the SFINAE would just name the type directly in a more roundabout way. Differential Revision: D18746633 fbshipit-source-id: 6da909834b511426b1cf7bbda0fd7643b5761f14
22d18f0b · Yedidya Feldblum · Facebook Github Bot · b1211e4c · 22d18f0b · 22d18f0b
Commit 22d18f0b authored Nov 30, 2019 by Yedidya Feldblum Committed by Facebook Github Bot Nov 30, 2019
3 changed files
--- a/folly/experimental/coro/AsyncGenerator.h
+++ b/folly/experimental/coro/AsyncGenerator.h
@@ -496,10 +496,6 @@ template <typename Reference, typename Value>
 inline constexpr bool is_async_generator_v<AsyncGenerator<Reference, Value>> =
    true;

-template <typename T>
-using enable_if_async_generator_t =
-    std::enable_if_t<detail::is_async_generator_v<T>, T>;
-
 } // namespace detail

 // Helper for immediately invoking a lambda with captures that returns an

--- a/folly/experimental/coro/Concat-inl.h
+++ b/folly/experimental/coro/Concat-inl.h
@@ -19,9 +19,16 @@
 namespace folly {
 namespace coro {

-template <typename Head, typename... Tail>
-detail::enable_if_async_generator_t<Head> concat(Head head, Tail... tail) {
-  using list = Head[];
+template <
+    typename HReference,
+    typename... TReference,
+    typename HValue,
+    typename... TValue>
+AsyncGenerator<HReference, HValue> concat(
+    AsyncGenerator<HReference, HValue> head,
+    AsyncGenerator<TReference, TValue>... tail) {
+  static_assert((std::is_same_v<decltype(head), decltype(tail)> && ...));
+  using list = AsyncGenerator<HReference, HValue>[];
  for (auto& gen : list{std::move(head), std::move(tail)...}) {
    while (auto val = co_await gen.next()) {
      co_yield std::move(val).value();

--- a/folly/experimental/coro/Concat.h
+++ b/folly/experimental/coro/Concat.h
@@ -42,8 +42,14 @@ namespace coro {
 //
 //    return result;
 //  }
-template <typename Head, typename... Tail>
-detail::enable_if_async_generator_t<Head> concat(Head head, Tail... tail);
+template <
+    typename HReference,
+    typename... TReference,
+    typename HValue,
+    typename... TValue>
+AsyncGenerator<HReference, HValue> concat(
+    AsyncGenerator<HReference, HValue> head,
+    AsyncGenerator<TReference, TValue>... tail);

 } // namespace coro
 } // namespace folly