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Lua的深拷贝和浅拷贝

今天在写游戏的时候,遇到了一个数据问题,就开始查资料

代码如下

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--- Deep copies a table into a new table.
-- Tables used as keys are also deep copied, as are metatables
-- @param orig The table to copy
-- @return Returns a copy of the input table
local function deep_copy(orig)
local copy
if type(orig) == "table" then
copy = {}
for orig_key, orig_value in next, orig, nil do
copy[deep_copy(orig_key)] = deep_copy(orig_value)
end
setmetatable(copy, deep_copy(getmetatable(orig)))
else
copy = orig
end
return copy
end

--- Copies a table into a new table.
-- neither sub tables nor metatables will be copied.
-- @param orig The table to copy
-- @return Returns a copy of the input table
local function shallow_copy(orig)
local copy
if type(orig) == "table" then
copy = {}
for orig_key, orig_value in pairs(orig) do
copy[orig_key] = orig_value
end
else -- number, string, boolean, etc
copy = orig
end
return copy
end

例子如下:
深拷贝

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local a = { aa = 1, bb = 2, cc = { dd = { ee = 3 } } }
--local b = deep_copy(a)
local b = shallow_copy(a)
b.cc.dd.ee = 111
b.bb = 111
ngx.say(cjson.encode(a))
ngx.say(cjson.encode(b))

结果:{“aa”:1,”bb”:2,”cc”:{“dd”:{“ee”:111}}}
{“aa”:1,”bb”:111,”cc”:{“dd”:{“ee”:111}}}

浅拷贝

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local men = { mkey = 555 }
local a = { aa = 1, bb = 2, cc = { dd = { ee = { ff = 3 } } } }
setmetatable(a, { __index = men })
local b = deep_copy(a)

ngx.say(a.cc.dd.ee.ff)
ngx.say(a.mkey)
ngx.say(b.mkey)

3
555
555

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