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

Subject: Re: [boost] [fusion] [intro] ADAPT_STRUCT extensions
From: Stefan Strasser (strasser_at_[hidden])
Date: 2010-08-15 10:22:12

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.

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

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