Sweet Snippet 系列之 Clone Lua Table

function clone(tbl)
  if type(tbl) ~= "table" then 
      return tbl 
  end
  local clone_tbl = {}
  for k, v in pairs(tbl) do
      clone_tbl[clone(k)] = clone(v)
  end
  return clone_tbl
end

local function clone_table_shallow(tbl)
    if type(tbl) ~= "table" then
        return tbl
    else
        local clone_table = {}
        for k, v in pairs(tbl) do
            clone_table[k] = v
        end
        return clone_table
    end
end

local function clone_table_recur(tbl, lookup_table)
    if type(tbl) ~= "table" then
        return tbl
    elseif lookup_table[tbl] then
        return lookup_table[tbl]
    end

    local new_table = {}
    lookup_table[tbl] = new_table
    for key, value in pairs(tbl) do
        new_table[clone_table_recur(key, lookup_table)] = clone_table_recur(value, lookup_table)
    end
    return new_table
end

local function clone_table_deep(tbl)
    local lookup_table = {}
    return clone_table_recur(tbl, lookup_table)
end

-- NOTE : 
-- 1. do not handle "metatable" now
-- 2. only support "table" clone
-- 3. it will influence by the "__pairs" metamethod
function clone(tbl, shallow_clone)
    if shallow_clone then
        return clone_table_shallow(tbl)
    else
        return clone_table_deep(tbl)
    end
end