[libsigcplusplus/c++17v4: 3/3] C++17: Replace call_*() helpers with std::apply().

[Murray Cumming <murrayc src gnome org>]

commit e497c86718bd2d158372ab59721e79032c84eb0d
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Sep 21 09:18:03 2016 +0200

    C++17: Replace call_*() helpers with std::apply().

 sigc++/adaptors/bind.h |   20 ++------------------
 sigc++/adaptors/hide.h |   17 +----------------
 sigc++/signal.h        |   12 +-----------
 3 files changed, 4 insertions(+), 45 deletions(-)
---
diff --git a/sigc++/adaptors/bind.h b/sigc++/adaptors/bind.h
index e93250b..0c281f0 100644
--- a/sigc++/adaptors/bind.h
+++ b/sigc++/adaptors/bind.h
@@ -151,9 +151,7 @@ struct bind_functor : public adapts<T_functor>
     const auto t_end = internal::tuple_end<t_args_size - I_location>(t_args);
     const auto t_with_bound = std::tuple_cat(t_start, t_bound, t_end);
 
-    constexpr const auto seq =
-      std::make_index_sequence<std::tuple_size<decltype(t_with_bound)>::value>();
-    return call_functor_operator_parentheses(t_with_bound, seq);
+    return std::apply(this->functor_, t_with_bound);
   }
 
   /** Constructs a bind_functor object that binds an argument to the passed functor.
@@ -168,12 +166,6 @@ struct bind_functor : public adapts<T_functor>
 private:
   /// The arguments bound to the functor.
   std::tuple<bound_argument<T_bound>...> bound_;
-
-  template <typename T, std::size_t... Is>
-  decltype(auto) call_functor_operator_parentheses(T&& tuple, std::index_sequence<Is...>)
-  {
-    return std::invoke(this->functor_, std::get<Is>(std::forward<T>(tuple))...);
-  }
 };
 
 /** Adaptor that binds argument(s) to the wrapped functor.
@@ -200,8 +192,7 @@ public:
     const auto t_bound = internal::tuple_transform_each<internal::TransformEachInvoker>(bound_);
     const auto t_with_bound = std::tuple_cat(t_args, t_bound);
 
-    constexpr auto seq = std::make_index_sequence<std::tuple_size<decltype(t_with_bound)>::value>();
-    return call_functor_operator_parentheses(t_with_bound, seq);
+    return std::apply(this->functor, t_with_bound);
   }
 
   /** Constructs a bind_functor object that binds an argument to the passed functor.
@@ -215,13 +206,6 @@ public:
 
   /// The argument bound to the functor.
   std::tuple<bound_argument<T_type>...> bound_;
-
-private:
-  template <typename T, std::size_t... Is>
-  decltype(auto) call_functor_operator_parentheses(T&& tuple, std::index_sequence<Is...>)
-  {
-    return std::invoke(this->functor_, std::get<Is>(std::forward<T>(tuple))...);
-  }
 };
 
 #ifndef DOXYGEN_SHOULD_SKIP_THIS
diff --git a/sigc++/adaptors/hide.h b/sigc++/adaptors/hide.h
index a6acdf3..8d9d145 100644
--- a/sigc++/adaptors/hide.h
+++ b/sigc++/adaptors/hide.h
@@ -102,28 +102,13 @@ struct hide_functor : public adapts<T_functor>
     const auto t_end = internal::tuple_end<size - index_ignore - 1>(t);
     const auto t_used = std::tuple_cat(t_start, t_end);
 
-    constexpr auto size_used = size - 1;
-
-    // TODO: Remove these? They are just here as a sanity check.
-    static_assert(std::tuple_size<decltype(t_used)>::value == size_used, "Unexpected t_used size.");
-
-    const auto seq = std::make_index_sequence<size_used>();
-    return call_functor_operator_parentheses(t_used, seq);
+    return std::apply(this->functor_, t_used);
   }
 
   /** Constructs a hide_functor object that adds a dummy parameter to the passed functor.
    * @param func Functor to invoke from operator()().
    */
   explicit hide_functor(const T_functor& func) : adapts<T_functor>(func) {}
-
-private:
-  // TODO_variadic: Replace this with std::experimental::apply() if that becomes standard
-  // C++, or add our own implementation, to avoid code duplication.
-  template <typename T_tuple, std::size_t... Is>
-  decltype(auto) call_functor_operator_parentheses(T_tuple& tuple, std::index_sequence<Is...>)
-  {
-    return std::invoke(this->functor_, std::get<Is>(tuple)...);
-  }
 };
 
 #ifndef DOXYGEN_SHOULD_SKIP_THIS
diff --git a/sigc++/signal.h b/sigc++/signal.h
index e6a6090..6b26cac 100644
--- a/sigc++/signal.h
+++ b/sigc++/signal.h
@@ -246,8 +246,7 @@ struct signal_emit
    */
   T_return operator()(const slot_type& slot) const
   {
-    const auto seq = std::make_index_sequence<std::tuple_size<decltype(a_)>::value>();
-    return call_call_type_operator_parentheses_with_tuple(slot, a_, seq);
+    return std::apply(slot, a_);
   }
 
   /** Executes a list of slots using an accumulator of type @e T_accumulator.
@@ -274,15 +273,6 @@ struct signal_emit
 
 private:
   std::tuple<type_trait_take_t<T_arg>...> a_;
-
-  // TODO_variadic: Replace this with std::experimental::apply() if that becomes standard
-  // C++, or add our own implementation, to avoid code duplication.
-  template <std::size_t... Is>
-  decltype(auto) call_call_type_operator_parentheses_with_tuple(
-    const slot_type& slot, const std::tuple<T_arg...>& tuple, std::index_sequence<Is...>) const
-  {
-    return std::invoke(slot, std::get<Is>(tuple)...);
-  }
 };
 
 /** Abstracts signal emission.