From: Daniel James (daniel_at_[hidden])
Date: 2005-10-10 13:54:34
Daniel James wrote:
> John Maddock wrote:
>>I'm not sure that would work unfortunately: if I have one library that uses
>>the TR1 <functional> and another that uses <boost/functional/hash.hpp> and
>>then include both libraries in my code, will they both work? Which
>>"version" of the hash lib do I get?
> The extensions would only be disabled if the user defines the macro, I
> don't think they should be disabled by default. If you're worried about
> ODR conflicts they can easily be avoided. The only cost is that the
> class is now specialized for the types mentioned in TR1, instead of just
> having a single definition.
I guess there is a problem with something like:
But this would really be against the intent of the macro - which is to
check that your code is not inadvertantly making use of the extensions.
I will suggest in the documentation that the macro is only used as a
compiler switch, and never in headers.
Or, I could just have two classes boost::hash & boost::tr1::hash (or
whatever). All of the implementation will still be in hash_value etc. so
there wouldn't be any code bloat. The macro would only affect
boost::tr1::hash, which would still include the extensions by default.
But that seems overly complicated.
Just so you understand what I'm getting at, here's some (untested and
probably incorrect) code.
template <class T> struct hash;
template <> struct hash<int>
: public std::unary_function<int, std::size_t>
std::size operator()(int v) const
template <class T> struct hash<T>
: public std::unary_function<T, std::size_t>
std::size operator()(T v) const
Can you see any other problems with it?
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