These are some macros to help build a traits class (for the parser/printer classes I am building).
Traits.h
#ifndef THORS_ANVIL_SERIALIZE_TRAITS_H
#define THORS_ANVIL_SERIALIZE_TRAITS_H
#include <string>
#include <tuple>
/*
* Macros for counting the number of arguments
* Currently set up for a max of 20.
*/
#define NUM_ARGS(...) NUM_ARGS_(0, __VA_ARGS__, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 09, 08, 07, 06, 05, 04, 03, 02, 01)
#define NUM_ARGS_(Zero, I1, I2, I3, I4 ,I5, I6, I7, I8, I9, I10, I11, I12, I13, I14, I15, I16, I17, I18, I19, I20, A, ...) A
/*
* Macros to quote the parameter
* Used below by the actions.
*/
#define QUOTE_(A) A
#define QUOTE(A) QUOTE_(#A)
/*
* Macro to force expansion of a macro that takes two parameters.
* Used by REP_*
*/
#define EXPAND_(Result) Result
#define EXPAND(Act, P1, P2) EXPAND_(Act(P1, P2))
/*
* Macros that that applies the action `Act` (a two parameter macro)
* To P1 (first argument)
* and a list of second arguments (placing a comma between each macro).
*
* Because NUM_ARGS is limited to 20, This expansion is also limited to 20
*/
#define REP_N(Act, P1, ...) REP_OF_N(Act, P1, NUM_ARGS(__VA_ARGS__), __VA_ARGS__)
#define REP_OF_N(Act, P1, Count, ...) REP_OF_N_(Act, P1, Count, __VA_ARGS__)
#define REP_OF_N_(Act, P1, Count, ...) REP_OF_ ## Count(Act, P1, __VA_ARGS__)
#define REP_OF_20(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_19(Act, P1, __VA_ARGS__)
#define REP_OF_19(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_18(Act, P1, __VA_ARGS__)
#define REP_OF_18(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_17(Act, P1, __VA_ARGS__)
#define REP_OF_17(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_16(Act, P1, __VA_ARGS__)
#define REP_OF_16(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_15(Act, P1, __VA_ARGS__)
#define REP_OF_15(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_14(Act, P1, __VA_ARGS__)
#define REP_OF_14(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_13(Act, P1, __VA_ARGS__)
#define REP_OF_13(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_12(Act, P1, __VA_ARGS__)
#define REP_OF_12(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_11(Act, P1, __VA_ARGS__)
#define REP_OF_11(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_10(Act, P1, __VA_ARGS__)
#define REP_OF_10(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_09(Act, P1, __VA_ARGS__)
#define REP_OF_09(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_08(Act, P1, __VA_ARGS__)
#define REP_OF_08(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_07(Act, P1, __VA_ARGS__)
#define REP_OF_07(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_06(Act, P1, __VA_ARGS__)
#define REP_OF_06(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_05(Act, P1, __VA_ARGS__)
#define REP_OF_05(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_04(Act, P1, __VA_ARGS__)
#define REP_OF_04(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_03(Act, P1, __VA_ARGS__)
#define REP_OF_03(Act, P1, P2, ...) EXPAND(Act, P1 ,P2), REP_OF_02(Act, P1, __VA_ARGS__)
#define REP_OF_02(Act, P1, P2, ...) EXPAND(Act, P1, P2), REP_OF_01(Act, P1, __VA_ARGS__)
#define REP_OF_01(Act, P1, P2) EXPAND(Act, P1, P2)
/*
* The actions we apply with REP_*
*
* TypeAction: Declares a type to hold the name and a pointer to the internal object.
* ValueAction: Declares an initialization of the Type putting the name and the pointer
* into the object
*/
#define TypeAction(Type, Member) std::pair<char const*, decltype(&Type::Member)>
#define ValueAction(Type, Member) { QUOTE(Member), &Type::Member }
/*
* Defines a trait for a user defined type.
* Lists the members of the type that can be serialized.
*/
#define ThorsAnvil_MakeTrait_Base(DataType, Parent, TType, ...) \
template<> \
class ::ThorsAnvil::Serialize::Traits<DataType> \
{ \
public: \
static constexpr TraitType type = TraitType::TType; \
Parent \
\
using Members = std::tuple< \
REP_N(TypeAction, DataType, __VA_ARGS__) \
>; \
\
static Members const& getMembers() \
{ \
static constexpr Members members{ \
REP_N(ValueAction, DataType, __VA_ARGS__) \
}; \
return members; \
} \
}; \
\
static_assert( \
::ThorsAnvil::Serialize::Traits<DataType>::type != ThorsAnvil::Serialize::TraitType::Invalid, \
"The macro ThorsAnvil_MakeTrait must be used outside all namespace." \
)
#define ThorsAnvil_MakeTrait(DataType, ...) \
ThorsAnvil_MakeTrait_Base(DataType, , Map, __VA_ARGS__)
#define ThorsAnvil_ExpandTrait(ParentType, DataType, ...) \
static_assert( \
std::is_base_of<ParentType, DataType>::value, \
"ParentType must be a base class of DataType"); \
static_assert( \
::ThorsAnvil::Serialize::Traits<ParentType>::type != ThorsAnvil::Serialize::TraitType::Invalid, \
"Parent type must have Serialization Traits defined" \
); \
ThorsAnvil_MakeTrait_Base(DataType, typedef ParentType Parent;, Parent, __VA_ARGS__)
/*
* Defines the generic type that all serialization types can expand on
*/
namespace ThorsAnvil
{
namespace Serialize
{
enum class TraitType {Invalid, Parent, Value, Map, Array};
template<typename T>
class Traits
{
public:
// By default if a traits type is not defined for a type
// You get this default implementation.
// This just says that it is invalid to serialize this type
// static_asserts sprinkled through the code will provide
// appropriate error messages based on this being invalid.
static constexpr TraitType type = TraitType::Invalid;
// For types that are Map/Array/Parent we can also define
// members that need be serialized via types. To achieve this
// they define a static getMembers() function.
// static Members const& getMembers()
//
// I would have made this a type declaration but I could
// not get it to bind correctly without an explicit
// instantiation (if you know how please let me know).
//
// So I use a static member function with a static variable
// which can be defined in-line within the traits class and
// does not need a separate declaration in a compilation unit.
} ;
/*
* Declare types that can be read/written directly by the parser/printer
* as value types. Other compound types need to use the Serializer/Deserializer
*/
template<> class Traits<short int> {public: static constexpr TraitType type = TraitType::Value;};
template<> class Traits<int> {public: static constexpr TraitType type = TraitType::Value;};
template<> class Traits<long int> {public: static constexpr TraitType type = TraitType::Value;};
template<> class Traits<long long int> {public: static constexpr TraitType type = TraitType::Value;};
template<> class Traits<unsigned short int> {public: static constexpr TraitType type = TraitType::Value;};
template<> class Traits<unsigned int> {public: static constexpr TraitType type = TraitType::Value;};
template<> class Traits<unsigned long int> {public: static constexpr TraitType type = TraitType::Value;};
template<> class Traits<unsigned long long int> {public: static constexpr TraitType type = TraitType::Value;};
template<> class Traits<float> {public: static constexpr TraitType type = TraitType::Value;};
template<> class Traits<double> {public: static constexpr TraitType type = TraitType::Value;};
template<> class Traits<long double> {public: static constexpr TraitType type = TraitType::Value;};
template<> class Traits<bool> {public: static constexpr TraitType type = TraitType::Value;};
template<> class Traits<std::string> {public: static constexpr TraitType type = TraitType::Value;};
}
}
#endif
The usage of this is:
#include "Traits.h"
class MyClass;
{
int x;
bool y;
std::string name;
friend class Traits<X>;
};
ThorsAnvil_MakeTrait(MyClass, x, y, name);
This then builds a Traits<MyClass> type that has all the information required for serialization (and de-serialization) of the class (into Json or Yaml or Binary).
template<>
class ::ThorsAnvil::Serialize::Traits<MyClass>
{
public:
static constexpr TraitType type = TraitType::Map;
using Members = std::tuple<
std::pair<char const*, int MyClass::*>,
std::pair<char const*, bool MyClass::*>,
std::pair<char const*, std::string MyClass::*>
>;
static Members const& getMembers()
{
static constexpr Members members{
{ "x", &MyClass::x },
{ "y", &MyClass::y },
{ "name", &MyClass::name }
};
return members;
}
};
static_assert(
::ThorsAnvil::Serialize::Traits<DataType>::type != ThorsAnvil::Serialize::TraitType::Invalid,
"The macro ThorsAnvil_MakeTrait must be used outside all namespace.");
