[boost] Re: abs and swap -or- overloading vs. specialization.

From: Valentin Bonnard (Bonnard.V_at_[hidden])
Date: 2000-01-29 15:10:46

John Maddock wrote:

> >I agree that it would be nice to allow overloading of functions in
> namespace
> >std.  However, in submitting a DR, it would be prudent to look at this and
> >other, if any, pitfalls, and propose restrictions on overloading and/or
> std
> >library design to avoid future problems.
> 
> There are other problems with overloading standard library functions

These aren't new. We already have them today, in the standard.

> #include <algorithm>
> #include <locale>
> 
> template <typename T> struct myUDT{};
> 
> namespace std
> {
> template <typename T, typename U>
> void fill(myUDT<T>*, myUDT<T>*, const U&){}
           ^
add <myUDT<T>*, U> here

> }
> 
> template <typename T>
> void g(T t)
> {
> }
> 
> void foo()
> {
>    std::fill<char*, char >(0, 0, 0);           // ambiguous

You don't mean char*, do you ?

How is it different w/ specialisation ?

> }
> 
> In each case there are workarounds, however the point here is that the
> presence of an overload in namespace std may prevent overwise perfectly
> legal C++ code from compiling - and that code could be in your standard
> library - in other words simply including a user-defined header that
> defines overloads in std can disable standard library code. 

That's correct. It would basically imply that lib code 
cannot use standard lib templates or function, only 
non-standard ones. And that's _not_ what we wanted. YADR.

> I'm not sure
> that the kind of usage given is all that likely (in fact I'm sure that its
> not), but even so, the standard seems to be correct when it says that
> overloads in std produce undefined behaviour.

???

It *seems* to be correct ? How could the Standard be wrong, 
since it is the Truth ?

-- 
Valentin Bonnard