From 9f50dd3308edca9164e37e4faec00ef767e2cd76 Mon Sep 17 00:00:00 2001
From: Paul <pfultz2@yahoo.com>
Date: Fri, 24 Apr 2015 21:19:52 -0500
Subject: [PATCH] Change args to take an integral constant, and make it return
 a function. Deprecate the old usage

---
 fit/args.h    | 40 ++++++++++++++++++++++++++++++++--------
 fit/lazy.h    |  2 +-
 test/args.cpp | 11 +++++++++--
 3 files changed, 42 insertions(+), 11 deletions(-)

diff --git a/fit/args.h b/fit/args.h
index 7e96853..7fb187a 100644
--- a/fit/args.h
+++ b/fit/args.h
@@ -18,19 +18,21 @@
 /// Description
 /// -----------
 /// 
-/// The `args` function returns the Nth argument passed to it. It actually
-/// starts at 1, so it is not the zero-based index of the argument.
+/// The `args` returns a function object that returns the Nth argument passed
+/// to it. It actually starts at 1, so it is not the zero-based index of the
+/// argument.
 /// 
 /// Synopsis
 /// --------
 /// 
-///     template<int N, class... Ts>
-///     constexpr auto args(Ts&&... xs);
+///     template<class IntegralConstant>
+///     constexpr auto args(IntegralConstant);
+/// 
 /// 
 /// Example
 /// -------
 /// 
-///     assert(args<3>(1,2,3,4,5) == 3);
+///     assert(args(std::integral_constant<int, 3>())(1,2,3,4,5) == 3);
 /// 
 
 namespace fit {
@@ -74,15 +76,37 @@ constexpr args_at<N...> make_args_at(seq<N...>)
     return {};
 }
 
+template<int N, class... Ts>
+constexpr auto get_args(Ts&&... xs) FIT_RETURNS
+(
+    make_args_at(typename gens<N>::type())(nullptr, make_perfect_ref(fit::forward<Ts>(xs))...)
+);
+
+template<class T, T N>
+struct args_f
+{
+    template<class... Ts>
+    constexpr auto operator()(Ts&&... xs) FIT_RETURNS
+    (
+        get_args<N>(fit::forward<Ts>(xs)...)
+    );
+};
+
 }
 
-// TODO: Make this a variable template in C++14
+// Deprecate
 template<int N, class... Ts>
 constexpr auto args(Ts&&... xs) FIT_RETURNS
 (
-    detail::make_args_at(typename detail::gens<N>::type())(nullptr, detail::make_perfect_ref(fit::forward<Ts>(xs))...)
+    detail::get_args<N>(fit::forward<Ts>(xs)...)
 );
 
+template<class IntegralConstant>
+constexpr detail::args_f<int, IntegralConstant::value> args(IntegralConstant)
+{
+    return detail::args_f<int, IntegralConstant::value>();
+}
+
 }
 
-#endif
\ No newline at end of file
+#endif
diff --git a/fit/lazy.h b/fit/lazy.h
index 9edfd73..84953f5 100644
--- a/fit/lazy.h
+++ b/fit/lazy.h
@@ -71,7 +71,7 @@ struct placeholder_transformer
     {
         template<class... Ts>
         constexpr auto operator()(Ts&&... xs) const FIT_RETURNS
-        (args<std::is_placeholder<T>::value>(fit::forward<Ts>(xs)...));
+        (detail::get_args<std::is_placeholder<T>::value>(fit::forward<Ts>(xs)...));
     };
 
     template<class T, typename std::enable_if<(std::is_placeholder<T>::value > 0), int>::type = 0>
diff --git a/test/args.cpp b/test/args.cpp
index b0aaee5..ff57af7 100644
--- a/test/args.cpp
+++ b/test/args.cpp
@@ -1,8 +1,15 @@
 #include <fit/args.h>
+#include <type_traits>
 #include "test.h"
 
+// FIT_TEST_CASE()
+// {
+//     FIT_STATIC_TEST_CHECK(fit::args<3>(1,2,3,4,5) == 3);
+//     FIT_TEST_CHECK( fit::args<3>(1,2,3,4,5) == 3 );
+// }
+
 FIT_TEST_CASE()
 {
-    FIT_STATIC_TEST_CHECK(fit::args<3>(1,2,3,4,5) == 3);
-    FIT_TEST_CHECK( fit::args<3>(1,2,3,4,5) == 3 );
+    FIT_STATIC_TEST_CHECK(fit::args(std::integral_constant<int, 3>())(1,2,3,4,5) == 3);
+    FIT_TEST_CHECK( fit::args(std::integral_constant<int, 3>())(1,2,3,4,5) == 3 );
 }
\ No newline at end of file