Re: [Boost-users] enable_if question

8 Jun 2004


      On Jun 7, 2004, at 7:11 PM, Hurd, Matthew wrote:
...
SFINAE does not kick in, because the condition 
(is_arithmeticstd::string::value) is not dependent on any template
arguments.

   Cheers, Jaakko
...
template< bool >
    typename boost::enable_if_c<
boost::is_arithmeticstd::string::value, void >::type
    exchange_code( boost::call_traitsstd::string::param_type
new_exchange_code )
    {
        lock lk(guard_ );
        exchange_code<false>( new_exchange_code);
    }
template< bool >
    typename boost::disable_if_c<
boost::is_arithmeticstd::string::value  , void >::type
    exchange_code( boost::call_traitsstd::string::param_type
new_exchange_code )
    {
        exchange_code<false>( new_exchange_code);
    }
Forget the relevance of the is_arithmetic bit, I use my own needs_lock
thingo.
For a start:
The compiler correctly identifies that ::type is not a member, but
SFINAE does not seem to kick in if I'm reading it correctly.
____________________
c:\source\matt\trading_engine\controller\instrument.hpp(66) : error
C2039: 'type' : is not a member of 'boost::enable_if_c'
        with
        [
            B=false,
            T=void
        ]
        c:\source\matt\trading_engine\controller\instrument.hpp(143) :
see reference to class template instantiation 'te::instrument<S>' being
compiled
____________________
template< bool >
    typename boost::disable_if_c<
boost::is_arithmeticstd::string::value  , void >::type
    exchange_code( boost::call_traitsstd::string::param_type
new_exchange_code )
    {
        exchange_code<false>( new_exchange_code);
    }
Is fine...
Flipping the conditions round by changing to is_arithmetic< int > flips
the failures around.
Same issue with the extra parameter approach:
template< bool >
    void
    exchange_code( boost::call_traitsstd::string::param_type
new_exchange_code,
    typename boost::enable_if_c< boost::is_arithmetic<int>::value, void
...
::type* dummy = 0  )
    {
        lock lk(guard_ );
        exchange_code<false>( new_exchange_code);
    }
template< bool >
    void
    exchange_code( boost::call_traitsstd::string::param_type
new_exchange_code,
    typename boost::disable_if_c< boost::is_arithmetic<int>::value  ,
void >::type* dummy = 0 )
    {
        exchange_code<false>( new_exchange_code);
    }
Is SFINAE meant to work in this way with member templates with
enable_if, vc7.1 and boost 1.31?
Something simple is probably escaping me...
Any thoughts?
Regards,
Matt Hurd.
_______________
Matt Hurd
+61.2.8226.5029
hurdm@sig.com
Susquehanna
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Re: [Boost-users] enable_if question

jajarvi