Can protobuf work with C++ templates?

[Ji Wan]

Suppose I have two message types `DoubleMatrix` and `FloatMatrix`, and a template class `Matrix`:


message DoubleMatrix {
  required uint32 rows = 1;
  required uint32 cols = 2;
  repeated double data = 3 [packed=true];
}


message FloatMatrix {
  required uint32 rows = 1;
  required uint32 cols = 2;
  repeated float data = 3 [packed=true];
}


template<typename DType>
class Matrix {
    MSTType mat_data_;
};



Is it possible to make `MSTType` as `FloatMatrix` if `DType` is `float`, as `DoubleMatrix` if `DType` is `double`?

[Stephen Tu]

This is not really a protobuf question, moreso a C++ question. But anyways, the typical way to do this is:

template <typename T> struct MatrixTraits { };

template <> struct MatrixTraits<double> { typedef DoubleMatrix type; };

template <> struct MatrixTraits<float>    { typedef FloatMatrix type; };

template <typename DType> class Matrix { 

    typename MatrixTraits<DType>::type mat_data_;

};

--
You received this message because you are subscribed to the Google Groups "Protocol Buffers" group.
To unsubscribe from this group and stop receiving emails from it, send an email to protobuf+u...@googlegroups.com.
To post to this group, send email to prot...@googlegroups.com.
Visit this group at http://groups.google.com/group/protobuf.
For more options, visit https://groups.google.com/d/optout.

[Ji Wan]

Got a new skill :P
Thanks very much!

--- Original Message ---

[Jui-Hsien Wang]

I am revoking this old question but I would like to know if protobuf can handle class templates?

Suppose I have a simple class

template<typename T>
struct Data {
    T data;
};

and know that T can only take on float and double. Is there a way to avoid writing two proto files?

On Wednesday, January 21, 2015 at 9:28:53 AM UTC-8, Stephen Tu wrote:

This is not really a protobuf question, moreso a C++ question. But anyways, the typical way to do this is:

template <typename T> struct MatrixTraits { };

template <> struct MatrixTraits<double> { typedef DoubleMatrix type; };

template <> struct MatrixTraits<float>    { typedef FloatMatrix type; };

template <typename DType> class Matrix { 

    typename MatrixTraits<DType>::type mat_data_;

};

On Mon, Jan 19, 2015 at 5:41 PM, Ji Wan <wa...@live.com> wrote:

Suppose I have two message types `DoubleMatrix` and `FloatMatrix`, and a template class `Matrix`:


message DoubleMatrix {
  required uint32 rows = 1;
  required uint32 cols = 2;
  repeated double data = 3 [packed=true];
}


message FloatMatrix {
  required uint32 rows = 1;
  required uint32 cols = 2;
  repeated float data = 3 [packed=true];
}


template<typename DType>
class Matrix {
    MSTType mat_data_;
};



Is it possible to make `MSTType` as `FloatMatrix` if `DType` is `float`, as `DoubleMatrix` if `DType` is `double`?

--
You received this message because you are subscribed to the Google Groups "Protocol Buffers" group.

To unsubscribe from this group and stop receiving emails from it, send an email to prot...@googlegroups.com.

[Adam Cozzette]

No, there is not really any good alternative but to write two separate message definitions. The .proto file format is language-agnostic so it can't use any C++-specific features.

To unsubscribe from this group and stop receiving emails from it, send an email to protobuf+u...@googlegroups.com.

To post to this group, send email to prot...@googlegroups.com.

Visit this group at https://groups.google.com/group/protobuf.
To view this discussion on the web visit https://groups.google.com/d/msgid/protobuf/056beefe-b2e1-4c79-8c44-b7027191eded%40googlegroups.com.

[Jui]

Yeah this actually makes sense. I just want to make sure I did not miss anything. Thanks.