How to iterate over and unsubscribe from all topics

[thorlancaster]

I am making a uWebSocket application where I have to be able to unsubscribe users from all subscribed topics. I am trying to do this with a lambda function (?) that iterates over all of a socket's subscribed topics, puts them into a std::vector (to avoid concurrent modification), and then unsubscribes from each one.

Here's what I have so far:
`void unsubscribeAll(uWS::WebSocket<true, true, PerSocketData> *ws){
std::vectorstd::string topics;

    ws->iterateTopics([](std::string topic){
        topics.push_back(topic);
    });

    for(int x = 0; x < topics.size(); x++){
        ws->unsubscribe(topics[x]);
    }
}`

Unfortunately, it's giving me an error: No viable conversion from '(lambda at /home/thor/lsd/Synchronizr.h:281:27)' to 'MoveOnlyFunction<void (std::string_view)>' (aka 'any_invocable<void (std::basic_string_view<char>)>')

How do I make the above code work? Currently I am storing the subscriptions in the userData, but that isn't optimal.

[ghost]

A university student working on project /home/thor/lsd/ brings me back 10 years, but I preferred mushrooms 🍄 😜

In any case - it's string_view not string

[thorlancaster]

@alexhultman Thank you for pointing that out. As a longtime Java programmer who has just started C++, I have a hard time following some of the errors, even with the help of CLion.

I managed to figure it out:

void unsubscribeAll(uWS::WebSocket<true, true, PerSocketData> *ws){
    std::vector<std::string> topics;
    ws->iterateTopics([&topics](std::string_view topic){
        std::string str = {topic.data(), topic.size()};
        topics.push_back(str);
    });
    for(const std::string& topic : topics){
        ws->unsubscribe(topic);
    }
}

Thank you again for your awesome library. It's already miles better than the Java WebSocket library that I used last year which randomly hung for a minute or so at the worst times.

P.S. LSD stands for Live Synchronizr Daemon. It's the server for a live sports stats feed and will be on my Github once it's feature-complete. Admittedly I have thought of 🌱 a few times when my C++ was misbehaving 😆