Question

I have a template looking like this:

struct add_node_value_visitor : boost::static_visitor<>
{
    add_node_value_visitor(){}

    template <typename T>
    void operator() ( const T& value) const
    {
        boost::lexical_cast<std::string, T>(value);
    }

};

The problem I have is that the visitor is used inside a for loop iterating over a bunch of values, and the resulting string of values needs to be one string, currently this would produce a bunch of separate strings, which is not what I want, so to solve this problem I thought I’d add a function pointer to the ctor of this struct so that I can pass in a function to concatenate the resulting string of each loop iteration and create one string. Then if I want to use this struct where I do not need a concatenation, I can still do that. The question is whether I should use a function pointer or is it possible to do this with something like boost::lambda?

Or would boost::function be easier to use?

Answer 1

Something like this?

struct add_node_value_visitor : public boost::static_visitor<>
{
public:
    typedef std::function<void(const std::string&)> concat_func_t;

    add_node_value_visitor(const concat_func_t& concat) : concat_(concat){}

    template <typename T>
    void operator() ( const T& value) const
    {
        concat_(boost::lexical_cast<std::string, T>(value));
    }

private:
    concat_func_t concat_;
};