utility: type_traits: use C++14 '_t' style

Add a foo_t variant of all type templates and refactor
usages to use the foo_t variant instead of `foo<...>::type`.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I67a597d5c0ced331398a5f4267504299bc351682
diff --git a/include/sdbusplus/asio/connection.hpp b/include/sdbusplus/asio/connection.hpp
index 6f01596..61c2583 100644
--- a/include/sdbusplus/asio/connection.hpp
+++ b/include/sdbusplus/asio/connection.hpp
@@ -130,8 +130,7 @@
                                  const InputArgs&... a)
     {
         using FunctionTuple = boost::callable_traits::args_t<MessageHandler>;
-        using FunctionTupleType =
-            typename utility::decay_tuple<FunctionTuple>::type;
+        using FunctionTupleType = utility::decay_tuple_t<FunctionTuple>;
         constexpr bool returnWithMsg = []() {
             if constexpr ((std::tuple_size_v<FunctionTupleType>) > 1)
             {
@@ -141,9 +140,8 @@
             }
             return false;
         }();
-        using UnpackType =
-            typename utility::strip_first_n_args<returnWithMsg ? 2 : 1,
-                                                 FunctionTupleType>::type;
+        using UnpackType = utility::strip_first_n_args_t<returnWithMsg ? 2 : 1,
+                                                         FunctionTupleType>;
         auto applyHandler = [handler = std::forward<MessageHandler>(handler)](
                                 boost::system::error_code ec,
                                 message::message& r) mutable {
@@ -270,7 +268,7 @@
         }
         else if constexpr (sizeof...(RetTypes) == 1)
         {
-            if constexpr (std::is_same<utility::first_type<RetTypes...>,
+            if constexpr (std::is_same<utility::first_type_t<RetTypes...>,
                                        void>::value)
             {
                 return;
@@ -278,7 +276,7 @@
             else
             {
                 // single item return
-                utility::first_type<RetTypes...> responseData{};
+                utility::first_type_t<RetTypes...> responseData{};
                 // before attempting to read, check ec and bail on error
                 if (ec)
                 {
diff --git a/include/sdbusplus/asio/object_server.hpp b/include/sdbusplus/asio/object_server.hpp
index 4fd04c7..1046272 100644
--- a/include/sdbusplus/asio/object_server.hpp
+++ b/include/sdbusplus/asio/object_server.hpp
@@ -53,21 +53,20 @@
 
 template <typename T>
 using FirstArgIsYield =
-    std::is_same<typename utility::get_first_arg<typename utility::decay_tuple<
-                     boost::callable_traits::args_t<T>>::type>::type,
+    std::is_same<utility::get_first_arg_t<
+                     utility::decay_tuple_t<boost::callable_traits::args_t<T>>>,
                  boost::asio::yield_context>;
 
 template <typename T>
 using FirstArgIsMessage =
-    std::is_same<typename utility::get_first_arg<typename utility::decay_tuple<
-                     boost::callable_traits::args_t<T>>::type>::type,
+    std::is_same<utility::get_first_arg_t<
+                     utility::decay_tuple_t<boost::callable_traits::args_t<T>>>,
                  message::message>;
 
 template <typename T>
 using SecondArgIsMessage = std::is_same<
-    typename utility::get_first_arg<
-        typename utility::strip_first_arg<typename utility::decay_tuple<
-            boost::callable_traits::args_t<T>>::type>::type>::type,
+    utility::get_first_arg_t<utility::strip_first_arg_t<
+        utility::decay_tuple_t<boost::callable_traits::args_t<T>>>>,
     message::message>;
 template <typename T>
 static constexpr bool callbackYields = FirstArgIsYield<T>::value;
@@ -124,8 +123,7 @@
 
   private:
     using CallbackSignature = boost::callable_traits::args_t<CallbackType>;
-    using InputTupleType =
-        typename utility::decay_tuple<CallbackSignature>::type;
+    using InputTupleType = utility::decay_tuple_t<CallbackSignature>;
     using ResultType = boost::callable_traits::return_type_t<CallbackType>;
     CallbackType func_;
     template <typename T>
@@ -145,9 +143,8 @@
     // optional message-first-argument callback
     int expandCall(message::message& m)
     {
-        using DbusTupleType = typename utility::strip_first_n_args<
-            details::NonDbusArgsCount<InputTupleType>::size(),
-            InputTupleType>::type;
+        using DbusTupleType = utility::strip_first_n_args_t<
+            details::NonDbusArgsCount<InputTupleType>::size(), InputTupleType>;
 
         DbusTupleType dbusArgs;
         if (!utility::read_into_tuple(dbusArgs, m))
@@ -231,8 +228,7 @@
 
   private:
     using CallbackSignature = boost::callable_traits::args_t<CallbackType>;
-    using InputTupleType =
-        typename utility::decay_tuple<CallbackSignature>::type;
+    using InputTupleType = utility::decay_tuple_t<CallbackSignature>;
     using ResultType = boost::callable_traits::return_type_t<CallbackType>;
     boost::asio::io_context& io_;
     CallbackType func_;
@@ -252,9 +248,8 @@
     // co-routine body for call
     void expandCall(boost::asio::yield_context yield, message::message& m)
     {
-        using DbusTupleType = typename utility::strip_first_n_args<
-            details::NonDbusArgsCount<InputTupleType>::size(),
-            InputTupleType>::type;
+        using DbusTupleType = utility::strip_first_n_args_t<
+            details::NonDbusArgsCount<InputTupleType>::size(), InputTupleType>;
         DbusTupleType dbusArgs;
         try
         {
@@ -559,11 +554,10 @@
     bool register_method(const std::string& name, CallbackType&& handler)
     {
         using ActualSignature = boost::callable_traits::args_t<CallbackType>;
-        using CallbackSignature = typename utility::strip_first_n_args<
+        using CallbackSignature = utility::strip_first_n_args_t<
             details::NonDbusArgsCount<ActualSignature>::size(),
-            ActualSignature>::type;
-        using InputTupleType =
-            typename utility::decay_tuple<CallbackSignature>::type;
+            ActualSignature>;
+        using InputTupleType = utility::decay_tuple_t<CallbackSignature>;
         using ResultType = boost::callable_traits::return_type_t<CallbackType>;
 
         if (initialized_)
@@ -601,8 +595,7 @@
     bool register_method(const std::string& name, CallbackType&& handler)
     {
         using CallbackSignature = boost::callable_traits::args_t<CallbackType>;
-        using InputTupleType =
-            typename utility::decay_tuple<CallbackSignature>::type;
+        using InputTupleType = utility::decay_tuple_t<CallbackSignature>;
         using ResultType = boost::callable_traits::return_type_t<CallbackType>;
 
         if (initialized_)
diff --git a/include/sdbusplus/utility/type_traits.hpp b/include/sdbusplus/utility/type_traits.hpp
index 51f5081..2031de4 100644
--- a/include/sdbusplus/utility/type_traits.hpp
+++ b/include/sdbusplus/utility/type_traits.hpp
@@ -14,7 +14,7 @@
  * @tparam Types - the parameter pack
  */
 template <typename... Types>
-using first_type = std::tuple_element_t<0, std::tuple<Types...>>;
+using first_type_t = std::tuple_element_t<0, std::tuple<Types...>>;
 
 /** @brief Convert T[N] to T* if is_same<Tbase,T>
  *
@@ -47,11 +47,17 @@
     using type = std::tuple<>;
 };
 
+template <std::size_t N, typename... Args>
+using strip_first_n_args_t = typename strip_first_n_args<N, Args...>::type;
+
 // Small helper class for stripping off the error code from the function
 // argument definitions so unpack can be called appropriately
 template <typename T>
 using strip_first_arg = strip_first_n_args<1, T>;
 
+template <typename T>
+using strip_first_arg_t = typename strip_first_arg<T>::type;
+
 // matching helper class to only return the first type
 template <typename T>
 struct get_first_arg
@@ -65,6 +71,9 @@
     using type = FirstArg;
 };
 
+template <typename... Args>
+using get_first_arg_t = typename get_first_arg<Args...>::type;
+
 // helper class to remove const and reference from types
 template <typename T>
 struct decay_tuple
@@ -76,6 +85,9 @@
     using type = std::tuple<typename std::decay<Args>::type...>;
 };
 
+template <typename... Args>
+using decay_tuple_t = typename decay_tuple<Args...>::type;
+
 // Small helper class for stripping off the first + last character of a char
 // array
 template <std::size_t N, std::size_t... Is>