[boost] Re: How to do this in with boost -- assert(typeid(T)==typeid(bool) )

From: Daniel Frey (d.frey_at_[hidden])
Date: 2003-01-09 15:02:23

On Thu, 09 Jan 2003 20:18:08 +0100, Derek Ross wrote:

> Daniel Frey wrote:
>> Uhm... don't know about MPL, but isn't this a good example for
>> type_traits? Something like:
>> 
>> template <class T>
>> bool SetOption(COptionInfo& o, const char* key, const T& value) {
>>         BOOST_STATIC_ASSERT( boost::is_same< T, bool >::value ||
>>                              boost::is_same< T, int >::value ||
>>                              boost::is_same< T, double >::value ||
>>                              boost::is_same< T, std::string >::value );
>>       ...etc...
> 
> It doesn't compile because the commas in the is_same template confuse
> the macro preprocessor.
> 
> The error message is:
> 
>   "macro "BOOST_STATIC_ASSERT" passed 5 arguments, but takes just 1"
> 
> Thought you might be interested...

Yes, sorry. I haven't tested this stuff, this is why I said "Something
like" ;)

Then how about:

template <class T>
bool SetOption(COptionInfo& o, const char* key, const T& value) {
        typedef boost::is_same< T, bool > is_bool_;
        typedef boost::is_same< T, int > is_int_;
        typedef boost::is_same< T, double > is_double_;
        typedef boost::is_same< T, std::string > is_string_;
        BOOST_STATIC_ASSERT( is_bool_::value ||
                             is_int_::value ||
                             is_double_::value ||
                             is_string_::value );
       ...etc...

(That's the "usual" work-around for the comma-in-macro problem :)

Regards, Daniel