PR77998 Remove std::thread::_Invoker::result_type

	PR libstdc++/77998
	* include/std/future (__future_base::_Deferred_state)
	(__future_base::_Async_state_impl): Use decltype to deduce return
	type, instead of _Invoker::result_type.
	* include/std/thread (thread::_Invoker::operator()): Likewise.
	(thread::_Invoker::result_type): Remove.

From-SVN: r241236

libstdc++-v3/ChangeLog

 2016-10-17  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/77998
+	* include/std/future (__future_base::_Deferred_state)
+	(__future_base::_Async_state_impl): Use decltype to deduce return
+	type, instead of _Invoker::result_type.
+	* include/std/thread (thread::_Invoker::operator()): Likewise.
+	(thread::_Invoker::result_type): Remove.
+
 	PR libstdc++/77987
 	* include/bits/unique_ptr.h (unique_ptr<T[], D>::reset<U>(U)): Copy
 	value to pointer of the correct type to swap, to support conversions

libstdc++-v3/include/std/future

@@ -561,10 +561,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     class _Async_state_commonV2;
 #endif
 
-    template<typename _BoundFn, typename = typename _BoundFn::result_type>
+    template<typename _BoundFn,
+	     typename _Res = decltype(std::declval<_BoundFn&>()())>
       class _Deferred_state;
 
-    template<typename _BoundFn, typename = typename _BoundFn::result_type>
+    template<typename _BoundFn,
+	     typename _Res = decltype(std::declval<_BoundFn&>()())>
       class _Async_state_impl;
 
     template<typename _Signature>

libstdc++-v3/include/std/thread

@@ -235,14 +235,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	using _Indices
 	  = typename _Build_index_tuple<tuple_size<_Tuple>::value>::__type;
 
-	using result_type
-	  = decltype(std::declval<_Invoker>()._M_invoke(_Indices()));
-
-	result_type
+	auto
 	operator()()
-	noexcept(noexcept(std::declval<_Invoker>()._M_invoke(_Indices())))
+	noexcept(noexcept(std::declval<_Invoker&>()._M_invoke(_Indices())))
+	-> decltype(std::declval<_Invoker&>()._M_invoke(_Indices()))
 	{ return _M_invoke(_Indices()); }
-
       };
 
     // Alias for _Invoker<tuple<DECAY_COPY(_Tp)...>>