Re: Review Request 59987: Added protobuf map support.

[Qian Zhang <zh...@gmail.com>]

> On Sept. 23, 2017, 7:14 a.m., Chun-Hung Hsiao wrote:
> > 3rdparty/stout/include/stout/protobuf.hpp
> > Line 607 (original), 640 (patched)
> > <https://reviews.apache.org/r/59987/diff/2/?file=1768786#file1768786line640>
> >
> >     How about a partial specialization for `google::protobuf::Map`?
> 
> Qian Zhang wrote:
>     Why do we need to do that? What do we want to achieve with such a partial specialization?
> 
> Chun-Hung Hsiao wrote:
>     For providing the `parse<google::protobuf::Map<K, V>>(const JSON::Value& value)` function. Say if we want to create a protobuf message `m` that contains a `map<string, string> map_field`, we cannot just do `m.mutable_map_field()->CopyFrom(parse<google::protobuf::RepeatedPtrField<...>(json))`. Instead we probably need something like `m.mutable_map_field()->swap(parse<google::protobuf::Map(json))`.
> 
> Chun-Hung Hsiao wrote:
>     Oh we probably cannot just apply `swap` on an r-value. But you know want I mean ;)

So you mean just like the partial specialization for `google::protobuf::RepeatedPtrField`:
```
template <typename T>
struct Parse<google::protobuf::RepeatedPtrField<T>>
```
We can add a partial specialization for `google::protobuf::Map`, right? I see there are a lot of places in our code to call the partial specialization for `google::protobuf::RepeatedPtrField`, but I am not sure if we have a need to call the partial specialization for `google::protobuf::Map` in our code.


- Qian


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On July 4, 2017, 10:43 a.m., Qian Zhang wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/59987/
> -----------------------------------------------------------
> 
> (Updated July 4, 2017, 10:43 a.m.)
> 
> 
> Review request for mesos, Anand Mazumdar and Zhitao Li.
> 
> 
> Bugs: MESOS-7656
>     https://issues.apache.org/jira/browse/MESOS-7656
> 
> 
> Repository: mesos
> 
> 
> Description
> -------
> 
> Map is a feature of proto2 syntax, but it can only be compiled
> with proto3 compiler, see the following discussion for details:
> https://groups.google.com/forum/#!topic/protobuf/p4WxcplrlA4
> We have already upgraded the compiler from 2.6.1 to 3.3.0 in
> MESOS-7228, however, to use protobuf map in Mesos code, we also
> need to add the protobuf map support to the code in Mesos for
> converting protobuf message to JSON object and parsing JSON
> object as protobuf message, that is what I have done in this patch.
> 
> 
> Diffs
> -----
> 
>   3rdparty/stout/include/stout/protobuf.hpp 15690b66cc4ae0c1bf2c2176d73c385ca75d3c20 
> 
> 
> Diff: https://reviews.apache.org/r/59987/diff/2/
> 
> 
> Testing
> -------
> 
> 
> Thanks,
> 
> Qian Zhang
> 
>