Re: [Boost-users] [lambda] extending lambda functions

Subject: Re: [Boost-users] [lambda] extending lambda functions
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-03-23 21:53:57

AMDG

alfC wrote:
> Ok, I gave up with Boost.Lambda for defining such "lazy function" and
> used Phoenix instead. The process was quite painless.  Below is the
> (working) code to define a lazy complex modulus function for those who
> are interested. I have still two concerns though:
>
> 1) I am worried how the lazy function can figure out which version of
> std::norm<T> to call to obtain the right result. For
> std::complex<double> the lazy function works fine (double is hard
> coded). But for std::complex<int> it seems that the lazy function will
> always convert the result to double, I couldn't make the lazy funcion
> as generic as the original std::norm<T>(std::complex<T> const& c)
> function. Is it possible to improve the lazy function definition in
> that respect?
> (BTW, for std::complex,    T == std::complex<T>::value_type)
>   

result is a template, so you just need to specialize it or use
some kind of metaprogramming (for instance Boost.Typeof).

> (It is not that I think std::complex<int> is useful for something but
> I thing it is a good example to ask about this).
>   

In fact, according to 26.2
"The effect of instantiating the template complex for any
type other than float, double or long double is unspecified."

> 2) I may be asking for too much sugar but is there a way to name the
> function "std::norm" and not have conflicts with the standard
> "std::norm<T>(std::complex<T> const& c)", the best I could do was to
> call it std::norm_;
>   

You're not allowed to put it in namespace std at all.

In Christ,
Steven Watanabe