Re: [Boost-users] Re: mpl related question

From: Istvan Buki (istvan.buki_at_[hidden])
Date: 2004-07-26 13:53:52

Hello David,

thanks for your clean and simple answer.
I also thought about something similar to your answer but I was wondering if 
there exist some way to calculate that index at compile-time. Looking at the 
assembly code generated, it doesn't make a big difference to my version where 
the index values are hard-coded but still...
In fact, the question I'm really trying to answer is: what is the price to pay 
(in term of performance and space) for using an mpl based solution compared 
to have my array elements initialized by a totally hard-coded function? Up to 
now what I've found is that my executable is 10% larger and the code is about 
4 times slower (again by looking at the assembly code generated).
So, if you can think of a more efficient solution I'm still interested.

Thanks,
Istvan
 
On Monday 26 July 2004 03:36, David Abrahams wrote:
> Istvan Buki <istvan.buki_at_[hidden]> writes:
> > Hello mpl experts,
> >
> > I'm trying to initialize the elements of an array using rules defined in
> > a list of structures. The code below illustrate what I'm trying to
> > achieve.
> >
> > The problem I have with this code is that the First_Descriptor structure
> > contain this index member that will be used to access the right item of
> > the array. This is not nice because it force the writer of this structure
> > to deal with implementation details. Is there a way to get rid of this
> > index typedef in the *_Descriptor structures by using another construct
> > from the mpl that would generate it ?
>
> The easiest thing to do is just to embed the index as a data member in
> the Initializer object, which can be stateful.  Just bump the index
> each time the Initializer is invoked.
>
> HTH,
> Dave