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: Frank Winter (fwinter_at_[hidden])
Date: 2016-04-14 10:37:47

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_
> {};
>

I had tried this

template<>
struct IsVector< Vector10 >
   : mpl::true_
{};

before. Same error message. Now I tried the base_of implementation

template<typename T, typename Enable = void >
struct IsVector
   : mpl::false_
{};

template<typename T>
struct IsVector<T , typename std::enable_if< std::is_base_of<Vector, 
T>::value >::type>
   : mpl::true_
{};

and still, I get basically the same error message:

/home/fwinter/src/boost_1_60_0/boost/proto/context/default.hpp:121:41: 
error: no match for ‘operator+’ (operand types are ‘Vector10’ and 
‘Vector10’)
          BOOST_PROTO_BINARY_DEFAULT_EVAL(+, proto::tag::plus, make, make)

It's weird since the operator+ should be there for Vector, and since I 
am importing the namespace VectorOps, it should work for derived 
classes. I don't see why it's not working.

Thanks,
Frank

>
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