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v1_0_cpp_versioning
msgpack-c have introduced API versioning mechanism.
MSGPACK_DEFAULT_API_VERSION means the default version of msgpack-c API. The current value is 1.
#if !defined(MSGPACK_DEFAULT_API_VERSION)
#define MSGPACK_DEFAULT_API_VERSION 1
#endifWhen you want to set MSGPACK_API_VERSION explicitly, give the macro value as follows:
g++ -DMSGPACK_API_VERSION=2
MSGPACK_DEFAULT_API_NS is a namespace name of the default msgpack version. It names 'v' + MSGPACK_DEFAULT_API_VERSION. e.g.) v1, v2, ...
It is used when you declare and define your custom overloads of operators.
See the following example:
https://github.com/msgpack/msgpack-c/blob/cpp-1.0.1/example/cpp03/class_non_intrusive.cpp#L28
https://github.com/msgpack/msgpack-c/blob/cpp-1.0.1/example/cpp03/class_non_intrusive.cpp#L67
MSGPACK_API_VERSION_NAMESPACE is a function style macro. It defines a namespace. You can pass an argument as the namespace you want to define.
MSGPACK_API_VERSION_NAMESPACE(v1) {
// ...
}
MSGPACK_API_VERSION_NAMESPACE(v2) {
// ...
}The macro is expanded to namespace. If the given namespace name is same as MSGPACK_DEFAULT_API_NS, the macro is expanded as follows:
In the case MSGPACK_DEFAULT_API_NS == v1
C++11
inline namespace v1 {
// ...
}
namespace v2 {
// ...
}C++03
namespace v1{}; using namespace v1; namespace v1 {
// ...
}
namespace v2 {
// ...
}It is used when you declare and define your custom overloads of operators.
See the following example:
https://github.com/msgpack/msgpack-c/blob/cpp-1.0.1/example/cpp03/class_non_intrusive.cpp#L28
https://github.com/msgpack/msgpack-c/blob/cpp-1.0.1/example/cpp03/class_non_intrusive.cpp#L67
When you want to adapt your class to msgpack-c, you have two choice. One is intrusive approach, the other is non-intrusive approach.
You just add MSGPACK_DEFINE macro on the public are of your class.
// Both ok.
#include <msgpack_fwd.hpp>
// or
#include <msgpack.hpp>
class your_class {
public:
your_class() {} // The class needs to be default constructible
// when you want to convert from msgpack::object
// to your_class.
your_class(int mem1, std::string const& mem2)
:mem1_(mem1), mem2_(mem2) {}
private:
// Data members can be private.
int mem1_;
std::string mem2_;
public:
// Define the following macro as public:
MSGPACK_DEFINE(mem1_, mem2_);
};
// When you include msgpack_fwd.hpp above, you need to include msgpack.h
// somewhere.
#include <msgpack.hpp>
Sometimes you can't modify the class you want to adapt msgpack-c. For example the class is a part of the third party library. You need to declrare and define operators as the following mannar:
// Include msgpack_fwd.hpp before your overloads are declared.
// Don't include msgpack.hpp here.
#include <msgpack_fwd.hpp>
// Declare the target class.
// Or include third_class_fwd.hpp if it's provided.
class third_class;
namespace msgpack {
MSGPACK_API_VERSION_NAMESPACE(MSGPACK_DEFAULT_API_NS) {
// Declare operators
// For convert third_class form msgpack::object.
object const& operator>> (msgpack::object const& o, third_class& v);
// For pack.
template <typename Stream>
packer<Stream>& operator<< (msgpack::packer<Stream>& o, third_class const& v);
// For create object::with_zone from third_class.
void operator<< (msgpack::object::with_zone& o, const third_class& v);
} // MSGPACK_API_VERSION_NAMESPACE(MSGPACK_DEFAULT_API_NS)
} // namespace msgpack
// Define third_class or include third_class.hpp.
class third_class {
public:
third_class() {} // The class needs to be default constructible
// when you want to convert from msgpack::object
// to third_class.
third_class(int mem1, std::string const& mem2)
:mem1_(mem1), mem2_(mem2) {}
// The class need to provide getter functions that return
// the values you want to pack.
int get_mem1() const { return mem1_; }
std::string get_mem2() const { return mem2_; }
private:
// Data members can be private.
int mem1_;
std::string mem2_;
};
// include msgpack.hpp after your overloads declared.
#include <msgpack.hpp>
namespace msgpack {
MSGPACK_API_VERSION_NAMESPACE(MSGPACK_DEFAULT_API_NS) {
// Declare operators after msgpack.hpp included
// For convert third_class form msgpack::object.
inline object const& operator>> (msgpack::object const& o, third_class& v) {
if (o.type != msgpack::type::ARRAY) throw msgpack::type_error();
if (o.via.array.size != 2) throw msgpack::type_error();
v = third_class(
o.via.array.ptr[0].as<int>(),
o.via.array.ptr[1].as<std::string>());
return o;
}
// For pack.
template <typename Stream>
inline packer<Stream>& operator<< (msgpack::packer<Stream>& o, third_class const& v) {
// packing member variables as an array.
o.pack_array(2);
o.pack(v.get_mem1());
o.pack(v.get_mem2());
return o;
}
// For create object::with_zone from third_class.
inline void operator<< (msgpack::object::with_zone& o, const third_class& v) {
o.type = type::ARRAY;
msgpack::object* p = static_cast<object*>(o.zone.allocate_align(sizeof(msgpack::object)*2));
o.via.array.ptr = p;
o.via.array.size = 2;
p[0] = msgpack::object(v.get_mem1(), o.zone);
p[1] = msgpack::object(v.get_mem1(), o.zone);
}
} // MSGPACK_API_VERSION_NAMESPACE(MSGPACK_DEFAULT_API_NS)
} // namespace msgpackYou only define operator<< (msgpack::object::with_zone& o, const third_class& v) overload only when you want to use msgpack::object::with_zone.
See this discussion.
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