introspection: add pointer-to-member name query

introspection/name.hpp

@@ -102,6 +102,72 @@ namespace cruft::introspection::name {
     template <> constexpr std::string_view bare<f64> (void) { return "f64"; }
 
 
+    ///////////////////////////////////////////////////////////////////////////////
+    namespace detail {
+        template <std::size_t N>
+        constexpr std::size_t
+        rfind (char const (&str)[N], char target)
+        {
+            static_assert (N > 1);
+
+            for (std::size_t i = N - 1; i; --i)
+                if (str[i] == target)
+                    return i;
+
+            return 0;
+        }
+    }
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    template <typename T>
+    struct pointer_to_member_type { };
+
+    template <typename A, typename B>
+    struct pointer_to_member_type<A B::*> { using type = A; };
+
+    template <typename T>
+    struct pointer_to_member_class { };
+
+    template <typename A, typename B>
+    struct pointer_to_member_class<A B::*> { using type = B; };
+
+
+
+    ///------------------------------------------------------------------------
+    /// Returns a stringview containing the name of the member pointed to by
+    /// the pointer-tomember.
+    template <typename TypeT, typename KlassT, TypeT KlassT::*Ptr>
+    constexpr std::string_view
+    member (void)
+    {
+        // __PRETTY_FUNCTION__
+        // GCC: "constexpr auto name() [with A = int; B = foo_t; A B::* member = &foo_t::abc]"
+        // clang: "auto name() [A = int, B = foo_t, member = &foo_t::abc]"
+        //
+        // The strategy is to count back from the end of the string to find
+        // the ampersand and return everything between that and the final
+        // character (which is always a ']').
+        constexpr std::size_t a = detail::rfind (__PRETTY_FUNCTION__, ':') + 1;
+        constexpr std::size_t b = detail::rfind (__PRETTY_FUNCTION__, ']');
+
+        constexpr std::string_view name = __PRETTY_FUNCTION__;
+        return std::string_view (name.data () + a, b - a);
+    }
+
+
+    template <auto Ptr>
+    constexpr std::string_view
+    member (void)
+    {
+        return member<
+            typename pointer_to_member_type <decltype(Ptr)>::type,
+            typename pointer_to_member_class<decltype(Ptr)>::type,
+            Ptr
+        > ();
+    }
+
+
     ///////////////////////////////////////////////////////////////////////////
     template <typename T>
     struct type_char;

test/introspection.cpp

@@ -195,5 +195,11 @@ int main ()
         "templated_with_enum"
     );
 
+    tap.expect_eq (
+        cruft::introspection::name::member<&foo::a> (),
+        std::string_view ("a"),
+        "pointer-to-member name"
+    );
+
     return tap.status ();
 }