Qi Symbols mapping to AST enum

Hello,

I've got a qi::symbols capturing some built-in types. At the moment, I
gather, they are mapped to std::string. However, I would rather map
them to an AST level enum.

For instance,

struct builtin_type_t : qi::symbols<char, std::string> {
    builtin_type_t() {
        this->add("double", "double")
            ("float", "float")
            // ...
            ;
    }
} builtin_type;

Instead,

namespace ast {
    enum type_t { type_double, type_float /* , ... */ };
}

struct builtin_type_t : qi::symbols<char, ast::type_t> {
    builtin_type_t() {
        this->add("double", ast::type_double)
            ("float", ast::type_float)
            // ...
            ;
    }
} builtin_type;

I assume this is possible? Am I missing something about that?

Thanks!

Michael Powell