Re: [boost] [fusion] [intro] ADAPT_STRUCT extensions

Subject: Re: [boost] [fusion] [intro] ADAPT_STRUCT extensions
From: Joel de Guzman (joel_at_[hidden])
Date: 2010-08-15 12:11:02

On 8/15/10 10:22 PM, Stefan Strasser wrote:
> Zitat von Joel de Guzman <joel_at_[hidden]>:
>>> the name caused both david and me to fundamentally misunderstand the
>>> macro, and I'm supposed to explain to the library user that it is the
>>> absolute wrong thing to do to adapt a class using ADAPT_CLASS.
>>
>> And I still don't understand the reason why. You mentioned that because
>> it does not return a reference it should not be called a "class" adaptor.
>> But I can't figure out why a reference to an actual object should
>> be a requirement.
>
> it isn't a sequence of values anymore but a sequence of objects that are
> convertible to the values. which can cause many subtle problems, among
> them probably some of the same as those of vector<bool>.
>
> one fusion-specific problem:
>
> struct A{
> int i;
> };
>
> struct F{
> void operator()(int) const{ /* do something */ }
> template<typename T>
> void operator()(T) const{}
> };
>
> fusion::for_each(A(),F()); //does something
> A a;
> fusion::for_each(a,F()); //does nothing.
>
> a "const" sequence is iterated as values, but a non-const sequence is
> iterated as proxy objects, which aren't matched to the "int"-overload.

Here's my use case (if I haven't given it yet). If you or anyone can
provide a better solution to what's provided, I'm all ears:

     class foo
     {
     public:

         int x() const;
         void x(int n);
         int y() const;
         void y(int n);

     private:
        // encapsulated
     };

Now, adapt that class to fusion.

>> Anyway... for the sake of moving forward, let me open the door to
>> name suggestions. I can probably suggest ADAPT_ADT.
>
> ADT?

Abstract Data Type.

> ADAPT_EXPR would be my suggestion, as it can also be used to make a
> fusion sequence out of some global variables for example.

Good point. But still doesn't cut it for me.

Regards,
-- 
Joel de Guzman
http://www.boostpro.com
http://spirit.sf.net