adding function example for is_constexpr

example/is_constexpr/function.cpp

@@ -0,0 +1,36 @@
+
+/*!
+Copyright (c) 2016 Barrett Adair
+
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+*/
+
+#include <type_traits>
+#include <callable_traits/callable_traits.hpp>
+
+// NOTE: Due to non-compliance in MSVC, is_constexpr always
+// returns std::false_type on that compiler, which causes
+// the static asserts below to fail.
+
+namespace ct = callable_traits;
+
+constexpr int foo(const int&) {
+    return 1;
+}
+
+int bar(const int&) {
+    return 1;
+}
+
+// for is_constexpr calls, function pointers must
+// be passed as std::integral_constants
+using F = std::integral_constant<decltype(&foo), &foo>;
+using B = std::integral_constant<decltype(&bar), &bar>;
+
+static_assert(ct::is_constexpr(F{}), "");
+static_assert(ct::is_constexpr<F>(), "");
+static_assert(!ct::is_constexpr(B{}), "");
+static_assert(!ct::is_constexpr<B>(), "");
+
+int main() { return 0; }