Re: [Boost-users] passing variable into template parameters.

From: Beth Jacobson (bethj_at_[hidden])
Date: 2006-05-02 10:58:27

Dale McCoy wrote:
> On 5/2/06, chun ping wang wrote:
>> Its more of a c++ question but i wonder how would I pass constant variables
>> into template parameters such as nth_index_iterator.
>>  Example: void func(const int& var)
>>  {
>>      nth_index_iterator<var>::type;
>>   }
>>
>>  Is this possible whats the work around this limitation?
> 
> Template parameters must be known at compile-time. If var is known at
> compile time, changing it to a #define should work. If var is not
> known at compile time, then you can't use it as a template parameter;
> you'll have to find something else that'll do the job (eg
> std::vector<bool> rather than std::bitmask<N>).
> 
> Strange tricks involving dynamic compiling and linking might work, but
> that would be several different types of difficult.
> 
> Dale

I've been working on something similar, and the best I've been able to 
come up with is this:

void func(const int& var)
{
     switch (var)
     {
     case 1:
         template_func<1>();
         break;
     case 2:
         template_func<2>();
         break;
     // etc
     }
}

If you have a limited range of var values, this should work fine. It's 
pretty tedious though, so if anyone can suggest an alternative not 
involving those "several different types of difficult", it would be much 
appreciated.

Beth