Re: [Boost-users] Strange bug : own function conflicts with MPL::size

From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-02-27 10:47:54

AMDG

Joel FALCOU wrote:
> Hi dear members,
>
> I'm currently working on some template based DSL using MPL and proto and 
> i came across
> some really strange problem.I'll try to give as much details as 
> possible, but I mus confess I'm really los so some important things may 
> have slipped.
>
> So, i have a class called matrix which is a simple end-user class for 
> handling multidimensionnal array of data. It's declared as follow :
>
> template<class T, class S = settings<> > class matrix : public 
> process_settings<T,S>::type;
>
> <snip>
>
> Now, this shape class is overloaded for each shape type by using 
> tempalte argument. For ex., the dense shape overload is given by
> shape<T,dense,options>, where T is the element of the matrix and options 
> the processed map of options. This class
> does all the grutn work of allocating, freeing and accessing elements. I 
> also have a method called size() that returns the size of the shape in 
> nbr of elment.
> matrix::size then just call back this size() method.
>
> Now I had the need to have a free function called size that take a 
> matrix and call .size() on it. Alas, the compiler don't let me do it 
> right :/
> Using gcc 4.1 (on linux or using mingw) i got the following error :
>
> <snip>
>
> Basically, instead of using my size() function, the compiler fetches 
> boost::mpl::size ...
> I checked and triple checked that i have NO using namespace boost 
> anywhere and that, if I rename size into let's say gimme_size, it works.
> It just fail at finding size cause he find the mpl structure instead. 
> Same for any function name like at or stuff like this (ie names that are 
> also a mpl class name).
> Now, if matrix ends up with only ONE tempalte arguments (ie T), it works 
> fine ...
>
> I'm completely lost. Even if i know that i can just rename this, i don't 
> want to just let it go. Either I did something stupid, either there is 
> some bug (I think the former alas) and i don't want such errors 
> resufraces later
> in some unrelated code. If details on the class actual definition is 
> needed, I'll post them.
>   

I would be helpful to see the definition of settings<>.
Are any of it's template parameters or base classes in namespace mpl?
Ok, yes.  I suspect that the compiler is finding mpl::size by ADL.  I 
don't think
it ought to, but I'll look it up.  I'd also like to know what happens 
with another compiler.

In Christ,
Steven Watanabe