Re: [boost] painless currying

Subject: Re: [boost] painless currying
From: Larry Evans (cppljevans_at_[hidden])
Date: 2011-08-26 19:34:04

On 08/26/11 17:56, Agustín K-ballo Bergé wrote:
> On 26/08/2011 15:04, Larry Evans wrote:
>> Since an n-dimensional array can be thought of as a function of
>> n indexes, I would think then that subscripting multi-dimensional
>> arrays would rub you the wrong way:
>>
>>    int f[1][1][1];
>>
>>    f[0] =>  doesn't return an int
>>    f[0][0] =>  doesn't return an int
>>    f[0][0][0] =>  *does*  return an int
>>
>> -regards,
>> Larry
>>
> 
> Now that you mention this, I have considered the same issue currently
> being discussed when trying to implement a multi-dimensional subscript
> operator facade. Initially I started invoking the function as soon as
> there were enough arguments (using Eric's technique); but then I
> considered several overloads with different number of arguments and the
> only solution I could came with was invoking the underlying function on
> a conversion operator, which would do more harm than good (specially
> considering C++0X auto). Eventually I simply had to discard this use
> case scenario. Then for curried functions, explicit invocation via ()
> seems like a viable solution to the problem.
> 
I encountered a somewhat similar problem when implementing a
multi-dimensional array where the number of dimensions was
determined only at run-time. Thus, the number of indices needed to get
an actual value out instead of a subarray was unknown until runtime.
As a workaround, both:

  operator[](undigned I)

and:

  operator()()

were defined for the array. The latter just assumed all the remaining
indices were 0 and returned that result.  The former (the operator[])
returned a subarray. I don't think there was any check for too many
indices (it was just a prototype).

Code is here:

http://svn.boost.org/svn/boost/sandbox/variadic_templates/sandbox/stepper/boost/array_stepper/array_own.hpp

-regards,
Larry