Re: [Boost-users] [fusion] BOOST_FUSION_DEFINE_STRUCT with user defined methods

Subject: Re: [Boost-users] [fusion] BOOST_FUSION_DEFINE_STRUCT with user defined methods
From: Joel de Guzman (djowel_at_[hidden])
Date: 2014-09-11 23:46:42

On 9/12/14, 12:52 AM, pfultz2 wrote:
>> Which would use the same techniques that Abel Sinkovics metaparse to
>> parse the struct and automatically expand to the boilerplate template
>> code for Boost.Fusion.
>
> I don't think metaparse can be used for this. It can't reference the members
> in the struct.
>
>> I'm naturally open for a first iteration in this direction to see how we
>> could change the DEFINE_STRUCT to allow adding own code to the structs
>> from your experience.
>
> As a first iteration, it would be nice if the extension metafunctions(ie
> `access::struct_member`, `struct_member_name`, `struct_assoc_key`) would
> provide an enable parameter. This would allow the struct definitions to be
> inline. Boost.Fusion already provides `INLINE_STRUCT` but it doesn't provide
> the member name nor an associative key.
>
> When we have the members inline, we can then inherit from the base operators
> we would like for the class:
>
>      struct person : equality<person>, streamable<person>
>      {
>          BOOST_FUSION_INLINE(
>              (std::string, name)
>              (int, age)
>          );
>      };
>
> And then we could have another `INLINE_CONSTRUCT` that will generate the
> constructor:
>
>      struct person : equality<person>, streamable<person>
>      {
>          BOOST_FUSION_INLINE_CONSTRUCT(person,
>              (std::string, name)
>              (int, age)
>          );
>      };
>
> Then for those that want a define all together, we could have a macro like
> this:
>
>      BOOST_FUSION_DEFINE(person, equality<person>, streamable<person>)
>      (
>          (std::string, name)
>          (int, age)
>      )
>
> So that way the user can add in the behaviours they want through
> inheritance.
>
> Additionally, we could also switch the type and field name order so we could
> handle types with commas in it:
>
>      struct person : equality<person>, streamable<person>
>      {
>          BOOST_FUSION_INLINE(
>              (name, std::string)
>              (age, int)
>              (locations, std::map<std::string, int>)
>          );
>      };
>
> Plus, by reversing the order we could handle the associative keys with same
> macro:
>
>      struct person : equality<person>, streamable<person>
>      {
>          struct keys
>          {
>              struct name {};
>              struct age {};
>              struct locations {};
>          }
>          BOOST_FUSION_INLINE(
>              (name, std::string, keys::name)
>              (age, int, keys::age)
>              (locations, std::map<std::string, int>, keys::locations)
>          );
>      };
>
> I could add some pull requests for this, starting with the enable
> parameters,
> if there is interest in something like this. Of course, this is difference
> than Damien's work, which looks it was making the type optional in the
> adapts
> macros.
>

I like this! Can we somehow merge this with Damien's work?

Regards,
-- 
Joel de Guzman
http://www.ciere.com
http://boost-spirit.com
http://www.cycfi.com/