//in the class definition
Rule(std::string name,
     std::vector<std::vector<std::shared_ptr<RuleMember>>> rules);
...

//in function 'main'
shared_ptr<Rule> expression(new Rule("expression", {
    { identifier },
    { expression, add, identifier }
}));

shared_ptr<Rule> expression(new Rule("expression", {
    { identifier },
    { shared_ptr<Rule> (expression), add, identifier }
}));