Re: [boost] [interest] Egg, function object builders and adaptors

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2008-01-17 06:47:54

Kirit Sælensminde wrote:
> shunsuke wrote:
>> Kirit Sælensminde wrote:
>>> And finally, does the curry function itself need to be a macro?
>> When you need static-initialization.
>> BOOST_EGG_CURRY2(..) is, in fact, a knotty braced initializer,
>> which guarantees static-initialization.
>>
>> Of course, Egg supports also:
>>
>>      typedef boost::result_of<T_curry2(int(*)(int,int))>::type T_curried_plus;
>>      T_curried_plus curried_plus = curry2(&::plus);
>>
>> No macros. But there is a function-call, which incurs dynamic-initialization.
>> You might notice that "static form" using macro and "dynamic form" using function
>> is nicely symmetric.
> 
> So the macro removed the first function call and actually writes a 
> function which is the curried version rather than perform the currying 
> at runtime? Now that *is* cool and seems to be a good enough reason to 
> have a macro (to me at least)! :)
> 
>>> Here is
>>> my implementation of curry2. I'd always assumed that a complete 
>>> implementation would overload on the relevant "callable" types:
>> As mentioned above, non-numbered form `curry` might support the famous "callables".
>> It seems difficult to define "what is famous", though.
> 
> There is another Boost library out in 1.35, Boost.FunctionTypes, which 
> might be able to help as it has decomposition functions that work with a 
> wider range of callable function than for example Boost.Function does. 
> Maybe that can be leveraged against? I've not had a chance to delve into 
> it myself yet though, but Tobias Schwinger seemed to think it would 
> handle the higher order requirements I was playing with last time I 
> raised it on the list.

No. It's basically just type traits to adapt built-in, Callable types to 
sequential interfaces (so they can be handled regardless of their arity
without using preprocessor metaprogramming).

Further, as mentioned in my post you cited, it provides a workaround for 
certain strange portability issues.

Regards,
Tobias