Porting addons to Classic

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Addons for Retail (8.1.5) can in most cases be easily ported to Classic (1.13.2) with minimal changes and removal of any non-Classic API.

For Vanilla (1.12) however, there is a bit more work involved.

Maps

Maps were reworked in Patch 8.0.1 and the stateful API was changed to be stateless.

• It's no longer needed to call SetMapToCurrentZone() first to get the current zone UI map, instead use C_Map.GetBestMapForUnit()

Combat Log

The combat log was reworked in Patch 2.4.0

• The event payload is returned from CombatLogGetCurrentEventInfo() since Patch 8.0.1
• See COMBAT_LOG_EVENT for details.

Frame Scripts

Most Vanilla addons still define their frames in XML, since CreateFrame() was only added in Patch 1.10

• Parameters like this, event and argN are no longer globals for the script handler. This was changed in Patch 4.0.1
• The this parameter was unique to WoW frame scripts. It can generally be replaced with self even though they are separate concepts.
• arg1, arg2, arg3, etc were replaced with the ... vararg. See the OnEvent frame script.

Quick fix

There are multiple ways to create frames and handle frame scripts in XML. For simplicity's sake we will only describe a quick fix and a Lua only example.

• Lua

function SomeAddon_OnLoad(frame)
	frame:RegisterEvent("ADDON_LOADED")
end

function SomeAddon_OnEvent(frame, event, addon)
	print(frame, event, addon)
end

• XML

<Frame name="SomeAddon">
	<Scripts>
		<OnLoad>
			SomeAddon_OnLoad(self)
		</OnLoad>
		<OnEvent>
			SomeAddon_OnEvent(self, event, ...)
		</OnEvent>
	</Scripts>
</Frame>

Lua only

It's also possible to create a frame and handle the scripts in Lua without use of XML, depending on how simple the addon is.

function f:OnEvent(event, addon)
	print(self, event, addon)
end

local f = CreateFrame("Frame")
f:RegisterEvent("ADDON_LOADED")
f:SetScript("OnEvent", f.OnEvent)

self parameter

For more information, see WowAce: Coding Tips#Methods and Ref Manual: Function Definitions

The following are the same for passing an argument.

function Object:Bravo() end
function Object.Bravo(self) end

The following are the same for calling a function.

Object:Bravo()
Object.Bravo(Object)