Error: 'std_srvs::Empty' is not a namespace

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Hey everyone,

I'm currently working through "A Gentle Introduction to ROS" and in the chapter about services the following example is shown:

bool toggleForward(std_srvs::Empty::Request &request, std_srvs::Empty::Response &response){...}

Now I don't want to write the std_srvs::Empty:: all the time and I tried the following:

using std_srvs::Empty::Request;
using std_srvs::Empty::Response;                                                                     

bool toggleForward(Request &request, Response &response){...}

But now I'm getting the following errors:

error: ‘std_srvs::Empty’ is not a namespace
 using std_srvs::Empty::Request;
                        ^

error: ‘std_srvs::Empty’ is not a namespace
 using std_srvs::Empty::Response;
                        ^
error: ‘Request’ was not declared in this scope
 bool toggleForward(Request &request, Response &response)
                    ^
 error: ‘request’ was not declared in this scope
 bool toggleForward(Request &request, Response &response)
                             ^
 error: ‘Response’ was not declared in this scope
 bool toggleForward(Request &request, Response &response)
                                      ^
error: ‘response’ was not declared in this scope
 bool toggleForward(Request &request, Response &response)
                                                ^

I don't understand what's happening here. For example, the following works:

using std::cout;

What is the difference between those two?