Fixed compilation for C++11

Author: breese

include/vista/constant_map.hpp

@@ -119,7 +119,8 @@ class constant_map
     constexpr value_compare value_comp() const noexcept;
 
 private:
-    static constexpr storage to_sorted(value_type (&&input)[N]) noexcept(vista::detail::is_nothrow_swappable<value_type>::value);
+    static VISTA_CXX14_CONSTEXPR
+    storage to_sorted(value_type (&&input)[N]) noexcept(vista::detail::is_nothrow_swappable<value_type>::value);
 
 private:
     // Error functions deliberately left non-constexpr to trigger compile-time error.
@@ -140,7 +141,8 @@ template <typename Key,
           typename T,
           std::size_t N,
           typename Compare = vista::less<Key>>
-constexpr auto make_constant_map(pair<Key, T> (&&input)[N]) noexcept(vista::detail::is_nothrow_swappable<decltype(*input)>::value) -> constant_map<Key, T, N, Compare>
+VISTA_CXX14_CONSTEXPR
+auto make_constant_map(pair<Key, T> (&&input)[N]) noexcept(vista::detail::is_nothrow_swappable<decltype(*input)>::value) -> constant_map<Key, T, N, Compare>
 {
     return constant_map<Key, T, N, Compare>{ std::forward<decltype(input)>(input) };
 }

include/vista/detail/constant_map.ipp

@@ -69,7 +69,8 @@ constexpr auto constant_map<K, T, N, C>::value_comp() const noexcept -> value_co
 }
 
 template <typename K, typename T, std::size_t N, typename C>
-constexpr auto constant_map<K, T, N, C>::to_sorted(value_type (&&input)[N]) noexcept(vista::detail::is_nothrow_swappable<value_type>::value) -> storage
+VISTA_CXX14_CONSTEXPR
+auto constant_map<K, T, N, C>::to_sorted(value_type (&&input)[N]) noexcept(vista::detail::is_nothrow_swappable<value_type>::value) -> storage
 {
     storage result {};
     vista::copy(input, input + N, result.begin());