> On Nov. 8, 2016, 8:38 a.m., Qian Zhang wrote:
> > I do not quite understand the intention of this patch. The description of 
> > this patch says that `Previously, the headers did not contain includes for 
> > any of the classes used in the file.`, but actually `stout/os.hpp` has been 
> > already included which almost has all the needed headers, like 
> > `stout/nothing.hpp`, `stout/try.hpp`, etc. So I guess the intention of this 
> > patch is to remove the inclusion of `stout/os.hpp` and instead include each 
> > needed headers directly, right? But I still see `stout/os.hpp` in both 
> > `utils.hpp` and `utils.cpp` in this patch which makes me a bit confused.
> 
> Joseph Wu wrote:
>     The style for our include headers is to include all dependencies, so that 
> changing the include headers of a dependency does not break any upstream code.
>     
>     i.e. 
>     foo.hpp:
>     ```
>     #include <string>
>     
>     typedef std::string Fooo;
>     ```
>     
>     bar.hpp:
>     ```
>     #include <map>
>     #include <string> // <- Need this because we use it in this file.
>     
>     #include "foo.hpp"
>     
>     std::map<Fooo, std::string> bar;
>     ```
>     
>     The exception is any headers that are effectively aliases to other 
> headers, like `stout/lambda.hpp` (to various `<functional>` types) or 
> `src/messages/messages.hpp` (to the protobuf `messages.pb.h`).

Thanks for the explanation! So if a header is needed by `utils.cpp`, then 
`utils.cpp` should always include it even it has already been included in 
`utils.hpp`.

And I have a further comment: in your updated patch, I see in `utils.cpp`, you 
include `stout/os.hpp` and also `stout/try.hpp`, `stout/nothing.hpp`, etc. 
which are actually already included in `stout/os.hpp`. I think that is not what 
we are doing in Mesos, if we have included `stout/os.hpp` in a .cpp, we do not 
need to include the header files in it again. See the following code as 
examples:
https://github.com/apache/mesos/blob/1.0.1/src/slave/containerizer/mesos/provisioner/backend.cpp#L19
https://github.com/apache/mesos/blob/1.0.1/src/slave/containerizer/docker.cpp#L38

Both of the above two files use `Try` and `Nothing`, but they only include 
`stout/os.hpp` not `stout/try.hpp` and `stout/nothing.hpp`.


- Qian


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On Nov. 8, 2016, 8:56 a.m., Joseph Wu wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/53556/
> -----------------------------------------------------------
> 
> (Updated Nov. 8, 2016, 8:56 a.m.)
> 
> 
> Review request for mesos, Benjamin Bannier, Jie Yu, and Qian Zhang.
> 
> 
> Bugs: MESOS-6360
>     https://issues.apache.org/jira/browse/MESOS-6360
> 
> 
> Repository: mesos
> 
> 
> Description
> -------
> 
> This fixes the headers in the provisioner utility.  Previously, the
> headers did not contain includes for any of the classes used in the
> file.
> 
> 
> Diffs
> -----
> 
>   src/slave/containerizer/mesos/provisioner/utils.hpp 
> 4efce0ed67312417495af8c884ce26ef6affaccb 
>   src/slave/containerizer/mesos/provisioner/utils.cpp 
> 340cf48819679cdd8d08d76dcd2328234477a15f 
> 
> Diff: https://reviews.apache.org/r/53556/diff/
> 
> 
> Testing
> -------
> 
> make check (OSX)
> make check (CentOS 7)
> msbuild ... (Windows 10)
> 
> 
> Thanks,
> 
> Joseph Wu
> 
>

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