Centralize transmission in PerformSend function

This means individual call sites trying to send messages out on the wire
don't each need to deal with duplicated details of state management
and correct processing of return values.

Also means some small docs can be added in-line, because someone's
going to look at the select trick and wonder what's going on in
a few years.

AceComm-3.0/ChatThrottleLib.lua

@@ -344,6 +344,20 @@ local function WasMessageThrottled(result)
 		or result == SendAddonMessageResult.ChannelThrottle
 end
 
+local function PerformSend(sendFunction, ...)
+	-- The select(-1, true, ...) incantation grabs the last return value
+	-- from the called function, defaulting to true if it returned nothing.
+	--
+	-- The default case is required for SendChatMessage. The selection of
+	-- the last return value is required due to per-flavor API divergences.
+
+	bMyTraffic = true
+	local sendResult = select(-1, true, sendFunction(...))
+	bMyTraffic = false
+
+	return MapToSendResult(sendResult)
+end
+
 function ChatThrottleLib:Despool(Prio)
 	local ring = Prio.Ring
 	while ring.pos and Prio.avail > ring.pos[1].nSize do
@@ -359,9 +373,7 @@ function ChatThrottleLib:Despool(Prio)
 			-- do nothing
 			sendResult = SendAddonMessageResult.NotInGroup
 		else
-			bMyTraffic = true
-			sendResult = MapToSendResult(select(-1, true, msg.f(unpack(msg, 1, msg.n))))
-			bMyTraffic = false
+			sendResult = PerformSend(msg.f, unpack(msg, 1, msg.n))
 		end
 
 		if WasMessageThrottled(sendResult) then
@@ -509,9 +521,7 @@ function ChatThrottleLib:SendChatMessage(prio, prefix,   text, chattype, languag
 	-- Check if there's room in the global available bandwidth gauge to send directly
 	if not self.bQueueing and nSize < self:UpdateAvail() then
 		self.avail = self.avail - nSize
-		bMyTraffic = true
-		_G.SendChatMessage(text, chattype, language, destination)
-		bMyTraffic = false
+		PerformSend(_G.SendChatMessage, text, chattype, language, destination)
 		self.Prio[prio].nTotalSent = self.Prio[prio].nTotalSent + nSize
 		if callbackFn then
 			-- We have no success/failure information here, and so may lie.
@@ -563,9 +573,7 @@ function ChatThrottleLib:SendAddonMessage(prio, prefix, text, chattype, target,
 	-- Check if there's room in the global available bandwidth gauge to send directly
 	if not self.bQueueing and nSize < self:UpdateAvail() then
 		self.avail = self.avail - nSize
-		bMyTraffic = true
-		local sendResult = MapToSendResult(select(-1, _G.C_ChatInfo.SendAddonMessage(prefix, text, chattype, target)))
-		bMyTraffic = false
+		local sendResult = PerformSend(_G.C_ChatInfo.SendAddonMessage, prefix, text, chattype, target)
 
 		if not WasMessageThrottled(sendResult) then
 			local didSend = (sendResult == SendAddonMessageResult.Success)