Proto for Boost mailing list page: Re: [proto] Transform result_of nightmare and preserving terminal identity

Subject: Re: [proto] Transform result_of nightmare and preserving terminal identity
From: Agustín K-ballo Bergé (kaballo86_at_[hidden])
Date: 2012-11-01 00:49:16

On 31/10/2012 05:28 p.m., Agustín K-ballo Bergé wrote:
> On 31/10/2012 04:59 p.m., Eric Niebler wrote:
>>> >I will
>>> >continue my research by implementing a custom evaluation context that
>>> >does this optimization 'on the fly', without actually modifying the
>>> >expression.
>  >
>> Evaluation contexts are weaker than transforms. If it can't be done with
>> a transform, it can't be done with a context. I can't tell from the code
>> fragment what exactly you're doing with the transforms you've written,
>> or whether they can be improved.
>
> Quoting from my original mail, what I want is to replace the following
> geometric vector expression:
>
>      p = q + r;
>
> by
>
>      p[0] = q[0] + r[0],
>      p[1] = q[1] + r[1],
>      ...,
>      p[N] = q[N] + r[N],
>      p;
>
> It **can** be done with a transform and that's what I did. The optimized
> proto expression evaluates ~33% faster than the original proto expression.
>
> I believe it can also be done with an evaluation context, that evaluates
> an expression N times with a component-wise evaluation context. A
> component-wise evaluation context would be a default context evaluation
> except that vector terminals are evaluated to one of its scalar components.
>
> Now that my transform finally works as intended, I will clean up the
> code and upload it somewhere for you and anyone interested to see it.

I have uploaded my experiment to https://github.com/eggs-cpp/eggs-la . 
It only implements what is needed for my research, there are wholes 
pretty much everywhere.

Agustín K-ballo Bergé.-
http://fusionfenix.com