[Boost-users] retrieving boost::variant values to different types

From: Andrew Chapman (andrew.chapman_at_[hidden])
Date: 2004-02-17 10:09:02

Hey everyone,

I was just having a look at the new boost::variant vlass, and I was 
expecting to be able to do something like:

     boost::variant<int, float> var;
     var = 5;

     int i   = boost::get<int>(var);   // fine
     float f = boost::get<float>(var); // throws

As the comments show, asking for the variant's value using get<int> 
works fine but get<float> throws an exception as it is an unmatched type.

So it seems that before you can retrieve the value of the variant you 
need to know its type? How do you check what type the variant is 
currently holding?

This would work but is inefficient/ugly:

     boost::variant<int, float> var;
     var = 5;

     std::stringstream str;
     str << var;

     int i   = atoi(str.str());
     float f = atof(str.str());

I was hoping to use the variant class to implement scripting language 
style variables where you can get/set them to be any type (which seems 
to work fine) and also retrieve them to any type (though retrieving a 
string as a bool may not always make too much sense).

Any suggestions?

-- 
Andrew Chapman
3D Technical Director - Framestore CFC