[PATCH] libstdc++: Simplify ranges::to closure objects

[Patrick Palka]

Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

-- >8 --

Use the existing _Partial range adaptor closure object in the
definition of ranges::to instead of essentially open coding it.

libstdc++-v3/ChangeLog:

	* include/std/ranges (__detail::_ToClosure): Replace with ...
	(__detail::_To): ... this.
	(__detail::_ToClosure2): Replace with ...
	(__detail::To2): ... this.
	(to): Simplify using the existing _Partial range adaptor
	closure object.
---
 libstdc++-v3/include/std/ranges | 140 ++++++++------------------------
 1 file changed, 32 insertions(+), 108 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 9d4c2e01c4d..33e576e563a 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1007,6 +1007,7 @@ namespace views::__adaptor
 
       // Invoke _Adaptor with arguments __r, _M_args... according to the
       // value category of this _Partial object.
+      // TODO: use explicit object functions ("deducing this").
       template<typename _Range>
 	requires __adaptor_invocable<_Adaptor, _Range, const _Args&...>
 	constexpr auto
@@ -1137,6 +1138,7 @@ namespace views::__adaptor
 
       // Invoke _M_rhs(_M_lhs(__r)) according to the value category of this
       // range adaptor closure object.
+      // TODO: use explicit object functions ("deducing this").
       template<typename _Range>
 	requires __pipe_invocable<const _Lhs&, const _Rhs&, _Range>
 	constexpr auto
@@ -9391,59 +9393,16 @@ namespace __detail
 /// @cond undocumented
 namespace __detail
 {
-  template<typename _Cont, typename... _Args>
-    class _ToClosure
-    : public views::__adaptor::_RangeAdaptorClosure<_ToClosure<_Cont, _Args...>>
+  template<typename _Cont>
+    struct _To
     {
-      tuple<decay_t<_Args>...> _M_bound_args;
-
-    public:
-      constexpr
-      _ToClosure(_Args&&... __args)
-      : _M_bound_args(std::forward<_Args>(__args)...)
-      { }
-
-      // TODO: use explicit object functions ("deducing this").
-
-      template<typename _Rg>
-	constexpr auto
-	operator()(_Rg&& __r) &
-	{
-	  return std::apply([&__r]<typename... _Tp>(_Tp&&... __args) {
-	    return ranges::to<_Cont>(std::forward<_Rg>(__r),
-				     std::forward<_Tp>(__args)...);
-	  }, _M_bound_args);
-	}
-
-      template<typename _Rg>
-	constexpr auto
-	operator()(_Rg&& __r) const &
-	{
-	  return std::apply([&__r]<typename... _Tp>(_Tp&&... __args) {
-	    return ranges::to<_Cont>(std::forward<_Rg>(__r),
-				     std::forward<_Tp>(__args)...);
-	  }, _M_bound_args);
-	}
-
-      template<typename _Rg>
-	constexpr auto
-	operator()(_Rg&& __r) &&
-	{
-	  return std::apply([&__r]<typename... _Tp>(_Tp&&... __args) {
-	    return ranges::to<_Cont>(std::forward<_Rg>(__r),
-				     std::forward<_Tp>(__args)...);
-	  }, std::move(_M_bound_args));
-	}
-
-      template<typename _Rg>
-	constexpr auto
-	operator()(_Rg&& __r) const &&
-	{
-	  return std::apply([&__r]<typename... _Tp>(_Tp&&... __args) {
-	    return ranges::to<_Cont>(std::forward<_Rg>(__r),
-				     std::forward<_Tp>(__args)...);
-	  }, std::move(_M_bound_args));
-	}
+      template<typename _Range, typename... _Args>
+      constexpr auto
+      operator()(_Range&& __r, _Args&&... __args) const
+      {
+	return ranges::to<_Cont>(std::forward<_Range>(__r),
+				 std::forward<_Args>(__args)...);
+      }
     };
 } // namespace __detail
 /// @endcond
@@ -9465,66 +9424,27 @@ namespace __detail
    */
   template<typename _Cont, typename... _Args>
     requires (!view<_Cont>)
-    constexpr __detail::_ToClosure<_Cont, _Args...>
+    constexpr auto
     to [[nodiscard]] (_Args&&... __args)
-    { return {std::forward<_Args>(__args)...}; }
+    {
+      using __detail::_To;
+      using views::__adaptor::_Partial;
+      return _Partial<_To<_Cont>, decay_t<_Args>...>{std::forward<_Args>(__args)...};
+    }
 
 /// @cond undocumented
 namespace __detail
 {
-  template<template<typename...> typename _Cont, typename... _Args>
-    class _ToClosure2
-    : public views::__adaptor::_RangeAdaptorClosure<_ToClosure2<_Cont, _Args...>>
+  template<template<typename...> typename _Cont>
+    struct _To2
     {
-      tuple<decay_t<_Args>...> _M_bound_args;
-
-    public:
-      constexpr
-      _ToClosure2(_Args&&... __args)
-      : _M_bound_args(std::forward<_Args>(__args)...)
-      { }
-
-      // TODO: use explicit object functions ("deducing this").
-
-      template<typename _Rg>
-	constexpr auto
-	operator()(_Rg&& __r) &
-	{
-	  return std::apply([&__r]<typename... _Tp>(_Tp&&... __args) {
-	    return ranges::to<_Cont>(std::forward<_Rg>(__r),
-				     std::forward<_Tp>(__args)...);
-	  }, _M_bound_args);
-	}
-
-      template<typename _Rg>
-	constexpr auto
-	operator()(_Rg&& __r) const &
-	{
-	  return std::apply([&__r]<typename... _Tp>(_Tp&&... __args) {
-	    return ranges::to<_Cont>(std::forward<_Rg>(__r),
-				     std::forward<_Tp>(__args)...);
-	  }, _M_bound_args);
-	}
-
-      template<typename _Rg>
-	constexpr auto
-	operator()(_Rg&& __r) &&
-	{
-	  return std::apply([&__r]<typename... _Tp>(_Tp&&... __args) {
-	    return ranges::to<_Cont>(std::forward<_Rg>(__r),
-				     std::forward<_Tp>(__args)...);
-	  }, std::move(_M_bound_args));
-	}
-
-      template<typename _Rg>
-	constexpr auto
-	operator()(_Rg&& __r) const &&
-	{
-	  return std::apply([&__r]<typename... _Tp>(_Tp&&... __args) {
-	    return ranges::to<_Cont>(std::forward<_Rg>(__r),
-				     std::forward<_Tp>(__args)...);
-	  }, std::move(_M_bound_args));
-	}
+      template<typename _Range, typename... _Args>
+      constexpr auto
+      operator()(_Range&& __r, _Args&&... __args) const
+      {
+	return ranges::to<_Cont>(std::forward<_Range>(__r),
+				 std::forward<_Args>(__args)...);
+      }
     };
 } // namespace __detail
 /// @endcond
@@ -9547,9 +9467,13 @@ namespace __detail
    * `r | std::ranges::to<std::vector>(an_allocator)`.
    */
   template<template<typename...> typename _Cont, typename... _Args>
-    constexpr __detail::_ToClosure2<_Cont, _Args...>
+    constexpr auto
     to [[nodiscard]] (_Args&&... __args)
-    { return {std::forward<_Args>(__args)...}; }
+    {
+      using __detail::_To2;
+      using views::__adaptor::_Partial;
+      return _Partial<_To2<_Cont>, decay_t<_Args>...>{std::forward<_Args>(__args)...};
+    }
 
 } // namespace ranges
 #endif // __cpp_lib_ranges_to_container
-- 
2.43.0.rc1