src/google/protobuf/proto_cast.h

// Protocol Buffers - Google's data interchange format
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#ifndef GOOGLE_PROTOBUF_UTIL_PROTO_CAST_H__
#define GOOGLE_PROTOBUF_UTIL_PROTO_CAST_H__

#include <string>

#include <google/protobuf/stubs/common.h>

// proto_cast<> is used to simulate over-the-wire conversion of one
// proto message into another.  This is primarily useful for unit tests
// which validate the version-compatibility semantics of protobufs.
// Usage is similar to C++-style typecasts:
//
// OldMessage old_message = /*...*/;
// NewMessage new_message = proto_cast<NewMessage>(old_message);
namespace google {
template<typename NewProto,
         typename OldProto>
NewProto proto_cast(const OldProto& old_proto) {
  string wire_format;
  GOOGLE_CHECK(old_proto.SerializeToString(&wire_format));

  NewProto new_proto;
  GOOGLE_CHECK(new_proto.ParseFromString(wire_format));
  return new_proto;
}

}  // namespace google
#endif  // GOOGLE_PROTOBUF_UTIL_PROTO_CAST_H__