AwesomeWM: for iterator is not callable (a table value) when iterating on clients

I'm trying to toggle all the titlebars when I press some keys. For this I want to iterate over all clients. I tries to do it several ways, including:

for s in screen do
 for c in s.clients do
  awful.titlebar.toggle(c)
 end
end

and

for c in client.get() do
 awful.titlebar.toggle(c)
end

Every time this code it executed I get an error: for iterator 'for iterator' is not callable (a table value).

This makes no sense to me. Can you explain why this happens and how to solve my problem?

I am running Awesome 4.3 with Lua 5.4.3.

Also, if you have an elegant way of toggling the titlebars that also impacts new clients, I'm taking. Thanks.

edit: I'd like to precise that the error occurs even without awful.titlebar.toggle(c) in the for-loops

Solution

@Piglet answer is correct, but here's the actual "how to fix it":

for index, c in ipairs(client.get()) do
    awful.titlebar.toggle(c)
end

The problem/confusion here is mostly historical. Someone made the screen into a loop iterator because they were thinking it was a cool time saver.

However, it is the only object in the whole API which work that way (and there wont be more). Other object use module_name() as a constructor, not a loop iterator. This is unfixable without breaking the API, so it persist. We cannot break APIs we document because it would break people configs when they upgrade.

Every other table/list in the AwesomeWM API requires either ipairs() or pairs() to iterate. ipairs is for ordered list/tables while pairs is for dictionaries.