Re: [boost] If boost::fusion is the hammer, then what's the nail?

From: Weapon Liu (weapon.liu_at_[hidden])
Date: 2006-12-14 09:15:16

John Maddock wrote:
> I have a piece of boilerplate code that accepts a tuple (of any size) and 
> prints out either a csv file or a boost::array C++ code conaining the data 
> passed.
>
> It allows me to output data for graphing, or matrixes of test data very 
> quickly just by creating a short function that returns a tuple, and then 
> passing that function to my boilerplate.  If I want more columns of data I 
> just increase the size of tuple by 1.
>
> I suppose I could have used a vector instead, but it's less elegant somehow.
>
> I've also used tuples in place of struct's whenever I have an API that needs 
> to return more than 2 items.  For example I have some root finding 
> algorithms that accept a unary functor whose root is to be found: the 
> functor returns a tuple containing the function evaluation, plus the first 
> two derivatives.  Using a tuple here simplified both implementation and 
> documentation. Had I felt the need, I could have performed compile time 
> dispatch to different algorithms based on how many derivatives were 
> available (the tuples size).
>   
Thanks John, that's very informative. Although a little bit of code 
would be excellent :-)

I do have a question about the second application, I mean, don't you 
have to wait until runtime to know how many derivatives a function 
actually have? Or is it just that it can be known in the very scenario 
you mentioned?