let co_invoke be defined in terms of tag_invoke

Summary: Currently there is an extension point `folly_co_invoke` for providing customizations for `co_invoke`. But `tag_invoke` is intended as a generic mechanism for providing namespaced customizations. So let us use that.

Reviewed By: ericniebler

Differential Revision: D26674580

fbshipit-source-id: b1baea04996f162699510c3aba8d2c330fcf34bb

folly/experimental/coro/AsyncGenerator.h

@@ -572,8 +572,8 @@ class FOLLY_NODISCARD AsyncGenerator {
   }
 
   template <typename F, typename... A, typename F_, typename... A_>
-  friend AsyncGenerator folly_co_invoke(
-      tag_t<AsyncGenerator, F, A...>, F_ f, A_... a) {
+  friend AsyncGenerator tag_invoke(
+      tag_t<co_invoke_type>, tag_t<AsyncGenerator, F, A...>, F_ f, A_... a) {
     auto r = invoke(static_cast<F&&>(f), static_cast<A&&>(a)...);
     while (auto v = co_await r.next()) {
       co_yield std::move(v).value();

folly/experimental/coro/Generator.h

@@ -255,7 +255,8 @@ class Generator {
   }
 
   template <typename F, typename... A, typename F_, typename... A_>
-  friend Generator folly_co_invoke(tag_t<Generator, F, A...>, F_ f, A_... a) {
+  friend Generator tag_invoke(
+      tag_t<co_invoke_type>, tag_t<Generator, F, A...>, F_ f, A_... a) {
     auto&& r = invoke(static_cast<F&&>(f), static_cast<A&&>(a)...);
     for (auto&& v : r) {
       co_yield std::move(v);

folly/experimental/coro/Invoke.h

@@ -22,10 +22,6 @@
 namespace folly {
 namespace coro {
 
-namespace invoke_detail {
-void folly_co_invoke(folly::detail::invoke_private_overload&);
-}
-
 //  co_invoke
 //
 //  This utility callable is a safe way to instantiate a coroutine using a
@@ -80,15 +76,18 @@ void folly_co_invoke(folly::detail::invoke_private_overload&);
 struct co_invoke_type {
   template <typename F, typename... A>
   FOLLY_ERASE constexpr auto operator()(F&& f, A&&... a) const
-      noexcept(noexcept(folly_co_invoke(
+      noexcept(noexcept(tag_invoke(
+          tag<co_invoke_type>,
           tag<invoke_result_t<F, A...>, F, A...>,
           static_cast<F&&>(f),
           static_cast<A&&>(a)...)))
-          -> decltype(folly_co_invoke(
+          -> decltype(tag_invoke(
+              tag<co_invoke_type>,
               tag<invoke_result_t<F, A...>, F, A...>,
               static_cast<F&&>(f),
               static_cast<A&&>(a)...)) {
-    return folly_co_invoke(
+    return tag_invoke(
+        tag<co_invoke_type>,
         tag<invoke_result_t<F, A...>, F, A...>,
         static_cast<F&&>(f),
         static_cast<A&&>(a)...);

folly/experimental/coro/Task.h

@@ -629,7 +629,8 @@ class FOLLY_NODISCARD Task {
   }
 
   template <typename F, typename... A, typename F_, typename... A_>
-  friend Task folly_co_invoke(tag_t<Task, F, A...>, F_ f, A_... a) {
+  friend Task tag_invoke(
+      tag_t<co_invoke_type>, tag_t<Task, F, A...>, F_ f, A_... a) {
     co_return co_await invoke(static_cast<F&&>(f), static_cast<A&&>(a)...);
   }