[Wobin]

I used the following in GuildLib

local visitedTables = {}
 
function LibGuildInfo:DeepTableCopy(source, subCall)
    local dest =  {}
    
    for k, v in pairs(source) do
        if type(v) == "table" and not visitedTables[v] then                     
            visitedTables[v] = true
            dest[k] = self:DeepTableCopy(v, true)            
        else
            dest[k] = v
        end
    end
    
    if not subCall then visitedTables = {} end
 
    return dest
end

It kept a list of table references in the external local, and just copied the reference if it had already been traversed.