Proto for Boost mailing list page: Re: [proto] Using a derived class as terminals in Boost.proto

Subject: Re: [proto] Using a derived class as terminals in Boost.proto
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2016-04-14 13:33:37

I'd try to use IsVector.
I'm not sure how to do this with a grammar (maybe someone can pitch in) but
you could do something like this

enable_if< IsVector<typename proto::result_of::value<Expr>::type> >

On 14 April 2016 at 18:04, Frank Winter <fwinter_at_[hidden]> wrote:

> I made some progress. If I specialize struct VectorSubscriptCtx::eval with
> Vector10, like
>
>
> struct VectorSubscriptCtx
> {
> VectorSubscriptCtx(std::size_t i) : i_(i) {}
>
> template<typename Expr, typename EnableIf = void>
> struct eval
> : proto::default_eval<Expr, VectorSubscriptCtx const>
> {};
>
> template<typename Expr>
> struct eval<
> Expr
> , typename boost::enable_if<
> proto::matches<Expr, proto::terminal< Vector10 > >
> >::type
> >
> {
> //..
> }
> };
>
> then it works (is was specialized with Vector). It also works when using
> the Boost _ literal (match anything), like
>
> template<typename Expr>
> struct eval<
> Expr
> , typename boost::enable_if<
> proto::matches<Expr, proto::terminal< _ > >
> >::type
>
>
> However, I feel this is not good style. Can this be expressed with the
> is_base_of trait instead?
>
>
>
>
>
> On 04/14/2016 10:10 AM, Mathias Gaunard wrote:
>
>> On 14 April 2016 at 14:43, Frank Winter <fwinter_at_[hidden]
>> <mailto:fwinter_at_[hidden]>> wrote:
>>
>>     Hi all!
>>
>>     Suppose you'd want to implement a simple EDSL (Embedded Domain
>>     Specific Language) with Boost.proto with the following requirements:
>>
>>          Custom class 'Vector' as terminal
>>          Classes derived from 'Vector' are working terminals too, e.g.
>>     Vector10
>>
>>     [...]
>>
>>     template<typename T>
>>     struct IsVector
>>        : mpl::false_
>>     {};
>>
>>
>>     template<>
>>     struct IsVector< Vector >
>>        : mpl::true_
>>     {};
>>
>>
>> Surely this should be true for all types derived from Vector.
>>
>> template<typename T, typename Enable = void>
>> struct IsVector
>>    : mpl::false_
>> {};
>>
>> template<typename T>
>> struct IsVector<T, typanem enable_if< is_base_of<Vector, T> >::type>
>>    : mpl::true_
>> {};
>>
>>
>> _______________________________________________
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>> http://lists.boost.org/mailman/listinfo.cgi/proto
>>
>>
>
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