[c++] Replace bond::check_method with decltype

The use of `bond::check_method` has been replaced with less restricting expression
SFINAE checks on supported compilers. 

Fixes #896

CHANGELOG.md

@@ -126,6 +126,8 @@ different versioning scheme, following the Haskell community's
 * Fixed a bug in `bond::nullable<T, Alloc>` where it was not propagating an allocator
   to `T` when `allocator_type` was not explicitly defined.
 * Fixed a bug in `bond::make_box` where `const T&` was not handled correctly.
+* The use of `bond::check_method` has been replaced with less restricting expression
+  SFINAE checks on supported compilers. [Issue #896](https://github.com/Microsoft/bond/issues/896)
 
 ### C# ###
 

cpp/inc/bond/core/config.h

@@ -16,16 +16,17 @@
 // BOND_SIMPLE_JSON_PROTOCOL disabled by default
 #endif
 
-#if defined(BOOST_NO_CXX11_NOEXCEPT) || defined(BOOST_NO_NOEXCEPT)
-#define BOND_NO_CXX11_NOEXCEPT
-#endif
-
 // std::once seems problematic on Linux (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60662)
 // For now we use std::call_once only on MSVC and boost::call_once on GCC/Clang.
 #if defined(BOOST_NO_CXX11_HDR_MUTEX) || !defined(_MSC_VER)
 #define BOND_NO_CX11_HDR_MUTEX
 #endif
 
+// MSVC 14 (VS 2015) has only a dangerous partial implementation of expression SFINAE.
+#if defined(BOOST_NO_SFINAE_EXPR) || (defined(_MSC_VER) && (_MSC_VER < 1910))
+#define BOND_NO_SFINAE_EXPR
+#endif
+
 #if defined(BOOST_NO_CXX14_RETURN_TYPE_DEDUCTION)
 #define BOND_NO_CXX14_RETURN_TYPE_DEDUCTION
 #endif

cpp/inc/bond/core/detail/mpl.h

@@ -17,11 +17,18 @@
 #include <utility>
 
 
-namespace bond
+namespace bond { namespace detail { namespace mpl
 {
 
-namespace detail { namespace mpl
+template <typename...> struct
+make_void
 {
+    using type = void;
+};
+
+template <typename... T>
+using void_t = typename make_void<T...>::type;
+
 
 template <typename T> struct
 identity
@@ -125,6 +132,4 @@ inline auto try_apply(F&& f)
 }
 
 
-}} // namespace mpl { namespace detail
-
-} // namespace bond
+} } } // namespace bond::detail::mpl

cpp/inc/bond/core/detail/omit_default.h

@@ -129,25 +129,40 @@ implements_field_omitting
     : std::false_type {};
 
 
+#ifdef BOND_NO_SFINAE_EXPR
 template <typename T> struct
 implements_field_omitting<T&>
     : implements_field_omitting<T> {};
+#endif
 
 
 // WriteFieldOmitted is an optional protocol writer method which is called for
 // omitted optional fields. It CAN be implemented by tagged protocols and MUST
 // be implemented by untagged protocols that allow omitting optional fields.
 template <typename Writer> struct
 implements_field_omitting<Writer,
-    typename boost::enable_if<bond::check_method<void (Writer::*)(BondDataType, uint16_t, const Metadata&), &Writer::WriteFieldOmitted> >::type>
+#ifdef BOND_NO_SFINAE_EXPR
+    typename boost::enable_if<check_method<void (Writer::*)(BondDataType, uint16_t, const Metadata&), &Writer::WriteFieldOmitted> >::type>
+#else
+    detail::mpl::void_t<decltype(std::declval<Writer>().WriteFieldOmitted(
+        std::declval<BondDataType>(),
+        std::declval<uint16_t>(),
+        std::declval<Metadata>()))>>
+#endif
     : std::true_type {};
 
 
 // ReadFieldOmitted is an optional protocol reader method which MUST be implemented
 // by untagged protocols that allow omitting optional fields.
 template <typename Input> struct
 implements_field_omitting<Input,
-    typename boost::enable_if<bond::check_method<bool (Input::*)(), &Input::ReadFieldOmitted> >::type>
+#ifdef BOND_NO_SFINAE_EXPR
+    typename boost::enable_if<check_method<bool (Input::*)(), &Input::ReadFieldOmitted> >::type>
+#else
+    typename boost::enable_if<std::is_same<
+        bool,
+        decltype(std::declval<Input>().ReadFieldOmitted())>>::type>
+#endif
     : std::true_type {};
 
 
@@ -198,19 +213,28 @@ implements_struct_begin_with_base
 
 template <typename Input> struct
 implements_struct_begin<Input,
-    typename boost::enable_if<bond::check_method<void (Input::*)(), &Input::ReadStructBegin> >::type>
+#ifdef BOND_NO_SFINAE_EXPR
+    typename boost::enable_if<check_method<void (Input::*)(), &Input::ReadStructBegin> >::type>
+#else
+    detail::mpl::void_t<decltype(std::declval<Input>().ReadStructBegin())>>
+#endif
     : std::true_type {};
 
 
 template <typename Input> struct
 implements_struct_begin_with_base<Input,
-    typename boost::enable_if<bond::check_method<void (Input::*)(bool), &Input::ReadStructBegin> >::type>
+#ifdef BOND_NO_SFINAE_EXPR
+    typename boost::enable_if<check_method<void (Input::*)(bool), &Input::ReadStructBegin> >::type>
+#else
+    detail::mpl::void_t<decltype(std::declval<Input>().ReadStructBegin(std::declval<bool>()))>>
+#endif
     : std::true_type {};
 
 
 // StructBegin
 template <typename Input>
-typename boost::enable_if<implements_struct_begin<Input> >::type
+typename boost::enable_if_c<implements_struct_begin<Input>::value
+                          && !implements_struct_begin_with_base<Input>::value>::type
 StructBegin(Input& input, bool /*base*/)
 {
     return input.ReadStructBegin();
@@ -234,7 +258,8 @@ StructBegin(Input& /*input*/, bool /*base*/)
 
 // StructEnd
 template <typename Input>
-typename boost::enable_if<implements_struct_begin<Input> >::type
+typename boost::enable_if_c<implements_struct_begin<Input>::value
+                          && !implements_struct_begin_with_base<Input>::value>::type
 StructEnd(Input& input, bool /*base*/)
 {
     return input.ReadStructEnd();

cpp/inc/bond/core/reflection.h

@@ -350,9 +350,15 @@ template <typename T, typename Enable = void> struct
 is_writer
     : std::false_type {};
 
-
 template <typename T> struct
-is_writer<T, typename boost::enable_if<check_method<void (T::*)(const Metadata&, bool), &T::WriteStructBegin> >::type>
+is_writer<T,
+#ifdef BOND_NO_SFINAE_EXPR
+    typename boost::enable_if<check_method<void (T::*)(const Metadata&, bool), &T::WriteStructBegin> >::type>
+#else
+    detail::mpl::void_t<decltype(std::declval<T>().WriteStructBegin(
+        std::declval<Metadata>(),
+        std::declval<bool>()))>>
+#endif
      : std::true_type {};
 
 

cpp/inc/bond/core/traits.h

@@ -114,6 +114,7 @@ get_protocol_writer<Reader<Input, MarshaledBondedProtocols>, Output>
 };
 
 
+// Used only for older compilers for which BOND_NO_SFINAE_EXPR is defined.
 template <typename T, T> struct
 check_method
     : std::true_type {};

cpp/inc/bond/protocol/encoding.h

@@ -21,7 +21,12 @@ implements_varint_write
 
 
 template <typename Buffer, typename T> struct
-implements_varint_write<Buffer, T, typename boost::enable_if<bond::check_method<void (Buffer::*)(T), &Buffer::WriteVariableUnsigned> >::type>
+implements_varint_write<Buffer, T,
+#ifdef BOND_NO_SFINAE_EXPR
+    typename boost::enable_if<check_method<void (Buffer::*)(T), &Buffer::WriteVariableUnsigned> >::type>
+#else
+    detail::mpl::void_t<decltype(std::declval<Buffer>().WriteVariableUnsigned(std::declval<T>()))>>
+#endif
     : std::true_type {};
 
 
@@ -73,7 +78,12 @@ implements_varint_read
 
 
 template <typename Buffer, typename T> struct
-implements_varint_read<Buffer, T, typename boost::enable_if<bond::check_method<void (Buffer::*)(T&), &Buffer::ReadVariableUnsigned> >::type>
+implements_varint_read<Buffer, T,
+#ifdef BOND_NO_SFINAE_EXPR
+    typename boost::enable_if<check_method<void (Buffer::*)(T&), &Buffer::ReadVariableUnsigned> >::type>
+#else
+    detail::mpl::void_t<decltype(std::declval<Buffer>().ReadVariableUnsigned(std::declval<T&>()))>>
+#endif
     : std::true_type {};