Hi,
I have a problem regarding the static visitor of boost::variant.
there is a variant and a mpl vector:
variant var;
typedef mpl::vector B_types;
the variant and the vector have the same number of types, but not the same
types.
I need to "visit" the element of the variant, and access the B_types element
at the same position as the element of the variant:
struct visitor : static_visitor<void>{
template<class A>
void operator()(A a) const{
typedef typename mpl::at_c::type B; //error
}
};
so if var.which() == 1, I need a typedef of type B2. obviously the code above
doesn't work because which() is a runtime function. but the value of which()
is known statically at this point (that's the point of visitation).
is there a way to access it, with boost::variant visitors?
I like neither of the solutions I can come up with:
1. write my own visitation pattern that not only instantiates the visitor with
the variant type but also with the vector type.
2.
convert the variant to
template
struct A_holder{
typedef B B_type;
A value;
};
variant,A_holder,A_holder > var;
3. do a seperate "visition" of the mpl vector inside the variant visitor:
struct visitor : static_visitor<void>{
template<class A>
void operator()(A a) const{
switch(var.which()){
case...
case...
}
}
};
is there a better way to do this?
