Use boost::any instead of (I)Value? about muparserx HOT 2 CLOSED

I don't want dependencies to any 3rd party library since this would be a major 
PITA. "Header only" in terms of boost usually means it depends on 100+ other 
boost header files. Apart from this boost::any is not a numeric type does not 
know how to add, subtract or multiply two instances of boost::any. Its not that 
i could add boost::any and the parser would magically know how to multiply two 
matrices wrapped in boost::any. 

> would magically know how to multiply two matrices wrapped in boost::any

That part wouldn't change, you would still have code like:

IValue& Value::operator*=(const IValue &val)
{
  if (IsScalar() && val.IsScalar()) {
    ...

but with support for many more types, e.g. (untested):

boost::any& boost::any::operator*=(const boost::any& rhs)
  if (this->type() == rhs.type() && this->type() == typeid(Matrix))
    ...

I would anyway prefer to use Eigen matrices which support all operators and 
also use expression templates to eliminate temporaries from expressions. Now 
the parsing of external types might be more difficult to implement. I guess 
what I'm after is the possibility for the user to specify the type to use for 
e.g. matrices so that this type would be used for storing the values of parsed 
matrix expressions. In that case muparser wouldn't have to have any code for 
math expressions, perhaps just do the check above to ensure both types are 
equal and call their own operators. The current matrix class could be e.g. the 
default template parameter to Value or IValue. Just something to consider in 
the long run...