Change type of a variable on function call

[masakk1]

How can this be done?

luasocket's udp has two states/types: connected and unconnected. Both of these have different functions available and will error out when calling one that isn't available by the other. However, whether the socket is connected or unconnected changes when a specific function is called, setpeername. Said function doesn't have a return value. For example:

local udp = socket.udp() --unconnected
udp:setpeername("10.0.0.1", port) --now the socket is connected! 

-- We can use functions from connected sockets
udp:send("packet")

-- But can't use functions from unconnected sockets
udp:sendto("packet", "10.0.0.2", 12345) --Error "expected unconnected socket, got {connected}"

The problem lies in: What type should the udp socket be in? Can I change it's type when calling setpeername?

Even if the latter was possible, I would still need to be able to check that: if the first argument for :setpeername() is "*" then it becomes unconnected.

The only way I can think of fixing it would be to do:

---@type UDPSocketUnconnected | UDPSocketConnected
local udp = socket.udp()

But it then won't know when certain functions can be called. Like in the example above, where udp:sendto() errors out.

[Josef-Friedrich]

Unfortunately I have no experience with socket.udp(). Maybe the problem you describe cannot be solved with a static type system. Are you describing a runtime problem?

Perhaps UDPSocketUnconnected | UDPSocketConnected should simply become UDPSocket?

[masakk1]

Unfortunately I have no experience with socket.udp(). Maybe the problem you describe cannot be solved with a static type system. Are you describing a runtime problem?

Perhaps UDPSocketUnconnected | UDPSocketConnected should simply become UDPSocket?

I think you hit the nail. It might just not be possible.

I've ultimately decided to return both (UDPSocketUnconnected | UDPSocketConnected). Unfortunately some functions are dependent on whether its connected or not, so I can't just return a generic.

Take a look at LuaCATS/luasocket#6.

[masakk1]

Apparently the TCP module also has this problem. They returned the Master type instead of Server | Client. Which makes a lot sense, but means that it this is required:

-- Create a TCP server and bind to a port.
local server = assert(socket.tcp())
server:bind("127.0.0.1", 12345)
---@cast server TCPSocketServer
server:listen(5)