a = {[1] = "a1", [2] = "a2", [3] = "a3", [5] = "a4", [6] = "a5",}
for key, value in ipairs(a) do
  print(key, value)
end


结果：
1	a1
2	a2
3	a3

a = {[1] = "a1", [2] = "a2", [3] = "a3", [5] = "a4", [6] = "a5",}
for key, value in pairs(a) do
  print(key, value)
end
结果：
6	a5
2	a2
3	a3
1	a1
5	a4

function clone( object )
local lookup_table = {}
local function copyObj( object )
if type( object ) ~= "table" then
return object
elseif lookup_table[object] then
return lookup_table[object]
end

local new_table = {}
lookup_table[object] = new_table
for key, value in pairs( object ) do
new_table[copyObj( key )] = copyObj( value )
end
return setmetatable( new_table, getmetatable( object ) )
end
return copyObj( object )
end

local t1 = { "a","b","c"}
-- local t2 = clone(t1);
--t1[1] = "abc";

local t2 = t1;
t1[1] = "abc";
for i=1,#t2 do
print(t2[i]);
end