Re: [boost] [metaparse] performance comparisons?

Subject: Re: [boost] [metaparse] performance comparisons?
From: Roland Bock (rbock_at_[hidden])
Date: 2015-06-07 11:51:41

On 2015-06-07 12:40, Evgeny Panasyuk wrote:
> 07.06.2015 12:07, Roland Bock:
>> However, this is limited in the way that the type cannot be based on a
>> literal outside a struct/class. There also is a macro that can be
>> employed to create such types, e.g:
>>
>> SQLPP_ALIAS_PROVIDER(hello);
>
> By the way, I saw sqlpp11 earlier, and I think that alias/field
> provider is a useful meta-programming tool on it's own.
> https://github.com/rbock/sqlpp11/blob/master/include/sqlpp11/alias_provider.h#L33-L48
>
>
> For example it can be used in transformation of vector of structs into
> structs of vectors - such macro would provide names for fields in
> synthesized struct of references.
>
> Perhaps it could be embedded by default into
> BOOST_FUSION_DEFINE_STRUCT and others.
>
>
> Also I think following template intrinsic can be useful addition to
> C++ ISO:
>
> template<char...> struct names_provider;
>
> Which would be automatically specialized by compiler on usage, for
> example something like:
>
> template<>
> struct names_provider<'f', 'o', 'o'>
> {
>     template<typename T>
>     struct field
>     {
>         T foo;
>     };
>     template<typename F>
>     struct method
>     {
>         template<typename ...Ts>
>         auto foo(Ts... args)
>         {
>             return F{}(args...);
>         }
>     };
>     // ...
> };

Right, I use this in sqlpp11 and sqlpp11-connector-stl (an experimental
SQL interface to vectors or other containers).

>
>
> With help of such intrinsic it is possible to parse string with some
> EDSL at compile time, and based only on this generate all required
> structures defined by language embedded in string.
It is still a PITA with the inheritance required to turn such things
into members of a struct.

I presented an idea of how to do this with much less pain here:

https://groups.google.com/a/isocpp.org/forum/#!msg/std-proposals/hYh3hWB0mwg/mDgCErbUXbMJ

Best,

Roland