`:setpeername()` doesn't care whether its connected or not. Contrary to `luasocket`'s documenation.

setpeername_doesnt_care.lua

local socket = require("socket")

-- Proof that `:setpeername()` doesn't care whether it's connected or not
-- On the other hand, `:getpeername()` errors if the UDP object isn't connected
local udp, err = socket.udp()
assert(udp, err)

local function print_peer(message)
	print(message)
	local success, result = pcall(udp.getpeername, udp)
	print("-> Result: ", success and result or "Can't get peer")
end

print_peer("unconnected clean")

print(udp:setpeername("127.0.0.1", 12345)) --1
print_peer("unconnected setting peer")

-- we can set a peer even when already connected
print(udp:setpeername("127.0.0.2", 12345)) --1
print_peer("connected setting another peer again")

print(udp:setpeername("*")) --1
print_peer("connected removing peer")

-- we can remove the specified peer even when already unconnected
print(udp:setpeername("*")) --1
print_peer("unconnected removing peer again")