RE: [boost] in search of a technique

From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2002-03-22 00:47:26

David Abrahams wrote:
> I'm looking for a legal way to cause certain constructs to fail to
> compile based on what templates have been instantiated at 
> that point in the program. The catch is that I also want it to be 
> legal to compile the same constructs in other translation units 
> (and, if I have to settle for something permissive, earlier in the 
> same translation unit) where the preventing templates have not 
> been instantiated. Most approaches to this problem result in 
> ODR violations, AFAIK. I'm thinking that there may be
> some promise in the use of the Barton & Nackmann trick in 
> combination with the unnamed namespace, but I'm not very 
> clear about it. 
> Has anyone already solved this puzzle?

I am not quote sure that I understood your requirements completely, but may
be something like this:

namespace {
template< typename T >
struct disable { typedef T type; };
}

template< typename T >
struct my
{
    my() { typedef typename disable<my>::type t; }
};

namespace {
template<> struct disable< my<int> >;
}

int main()
{
    my<long> m1; // ok
    my<int> m2; // error
    return 0;
}

?

Aleksey