[SDPhantom]

I might as well post mine, I have many versions of this and I don't even know if this is the latest one. I keep recreating it for every addon I need it in.

local Name,Addon=...;
 
local C_Timer_After=C_Timer.After;
local next=next;
local pairs=pairs;
local setmetatable=setmetatable;
local tostring=tostring;
local type=type;
 
--------------------------
--[[    Event Frame ]]
--------------------------
local function OnEvent(self,event,...)
    local list=self[event];
    if list and next(list) then
        for funcobj in pairs(list) do funcobj[0](funcobj,event,...); end
    else
        self:UnregisterEvent(event);
    end
end
 
local EventFrame=CreateFrame("Frame");
EventFrame:SetScript("OnEvent",OnEvent);
 
------------------------------------------
--[[    Callback Object Registry    ]]
------------------------------------------
local CallbackMeta={__index={},__call=function(t,...) return t[0](t,...); end};
local FuncObject=setmetatable({},{__index=function(t,k) local obj=setmetatable({[0]=k},CallbackMeta); t[k],t[obj]=obj,obj; return obj; end});
 
function CallbackMeta.__index:RegisterEvent(...)--  Obj:RegisterEvent(Event<s>) -or-    Addon.RegisterEvent(Func/Obj,Event<s>)
    self=FuncObject[self];--    Make sure we have our custom object (Can be used as an AddOn API call)
 
    for i=1,select("#",...) do
        local event=tostring(select(i,...)):upper();
 
        local list=EventFrame[event];
        if not list then list={}; EventFrame[event]=list; end
        if not list[self] then
            list[self]=true;
            EventFrame:RegisterEvent(event);
        end
    end
 
    return self;
end
 
function CallbackMeta.__index:UnregisterEvent(...)--    Obj:UnregisterEvent(Event<s>)   -or-    Addon.UnregisterEvent(Func/Obj,Event<s>)
    self=FuncObject[self];--    Make sure we have our custom object (Can be used as an AddOn API call)
    local argcount=select("#",...);
 
    if argcount>0 then
        for i=1,argcount do
            local event=tostring(select(i,...)):upper();
 
            local list=EventFrame[event];
            if list then
                list[self]=nil;
                if not next(list) then EventFrame:UnregisterEvent(event); end
            end
        end
    else
        for i,j in pairs(EventFrame) do
            if type(j)=="table" then j[self]=nil; end
        end
    end
 
    return self;
end
 
function CallbackMeta.__index:DelayedCall(delay) C_Timer_After(delay,self[0]); end
 
----------------------------------
--[[    API Registration    ]]
----------------------------------
Addon.RegisterEvent=CallbackMeta.__index.RegisterEvent;
Addon.UnregisterEvent=CallbackMeta.__index.UnregisterEvent;
function Addon.FireEvent(event,...) OnEvent(EventFrame,tostring(event):upper(),...); end
function Addon.GetCallbackObject(func) return FuncObject[func]; end