Itch.io and coroutines

The Defoldmine
#1

This is a really nice article advocating the use of Lua coroutines and how they are used in OpenResty (a Lua based web server used by itchi.io): http://leafo.net/posts/itchio-and-coroutines.html

Coroutines are particularly nice to use when you write a lot of asynchronous code such as client APIs communicating with a backend service From a game developers point of view they can be used to execute computationally heavy things such as pathfinding and complex AI algorithms over several frames. They can also be used to simplify things such as tutorials, cut scenes and dialogue systems.

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#2

Why can’t I just do all that with functions?

#3

Well of course you can use functions and you still do when you work with coroutines. The difference is how you deal with long running or asynchronous tasks. You can either use coroutines or make them callback or message based. Personally I prefer the way coroutines can make asynchronous code look synchronous. Take the example presented in the article I linked above:

function getUserProfileLinks(userId) {
  query("select * from users where id = ? limit 1", userId, function(users) {
    query("select * from profiles where user_id = ? limit 1", users[0].id, function(profiles) {
      query("select * from profile_links where profile_id = ?", profile.id, function(links) {
        // return links??
      })
    })
  })

  // ?? can't return here since everything is async, see above
}

This looks messy and there is no way those asynchronous function calls can return a value when getUserProfileLinks() is called. The same function implemented with the use of coroutines would look like this:

function getUserProfileLinks(user_id)
  local users = query("select * from users where id = ? limit 1", user_id)
  local profiles = query("select * from profiles where user_id = ? limit 1", users[1])
  return query("select * from profile_links where profile_id = ?", profiles[1])
end

Here the query function takes the asynchronous task of getting data from a database and makes it look synchronous. And all of a sudden the getUserProfileLinks() function can actually return links when called.

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