C++ Why use an implicit conversion from (std::string) to (void) type?

Question

I'm looking at CPP-NETLIB's source code and came across this syntax where it describes the concepts.

template <class R> struct ClientRequest : network::Message<R> {
  BOOST_CONCEPT_USAGE(ClientRequest) {
    std::string tmp;
    R request_(tmp);
    swap(request, request_);  // swappable via ADL

    std::string host_ = host(request);
    boost::uint16_t port_ = port(request);
    std::string path_ = path(request);
    std::string query_ = query(request);
    std::string anchor_ = anchor(request);
    std::string protocol_ = protocol(request);

    request << uri(std::string());

    network::http::uri(request, std::string());

    (void) host_;
    (void) port_;
    (void) path_;
    (void) query_;
    (void) anchor_;
    (void) protocol_;
  }

 private:
  R request;
};

I can't seem to find any explanations that describe how the (void) conversion of in-scope types could be necessary or what it would do. Why would you need to clear the stack before ending the BOOST_CONCEPT_USAGE member function? What else would it do if not clearing the stack?

Answer 1

It's just for suppressing the compiler's warnings about unused variable, nothing special.

It does NOT clear the stack in any way, if that's what you mean.