lua table引用问题

一，基础

1，在lua中，table只是传递引用（即两个变量都指向同一片内存空间），所以不能用简单的 "=" 来copy两个表，并试图修改一个表中的值。

tb = {}tb.a = 11tb.b = 22tb_ref = tbfunction p(tip)  print("--------------------------"  .. tip)  print("tb.a = " .. tb.a .. "    " .. "tb.b = " .. tb.b)  print("tb_ref.a = " .. tb_ref.a .. "    " .. "tb_ref.b" .. tb_ref.b)endp("原始")tb_ref.a = 33p("修改了引用的a = 33，原来的a也变了")tb.b = 44p("修改了原始的b = 44，引用的b也变了")print("----------------------非表test")a = 1c = ac = 3print("a = " .. a)print("c = " .. c) 打印结果：--------------------------原始tb.a = 11    tb.b = 22tb_ref.a = 11    tb_ref.b22--------------------------修改了引用的a = 33，原来的a也变了tb.a = 33    tb.b = 22tb_ref.a = 33    tb_ref.b22--------------------------修改了原始的b = 44，引用的b也变了tb.a = 33    tb.b = 44tb_ref.a = 33    tb_ref.b44----------------------非表testa = 1c = 3

结果：

当改变表的一个值以后，它的引用的值也发生了变化；

对于非表的一般常数来说，它的赋值不存在引用的问题；

2，table存储

1）table里保存数据，数据可以是任何类型，包括function。

2）table里也可以保存table

3）key代表数据存储的位置

4）value就是用特定的key存储的数据

二，记录遇见的一个关于table的问题

代码如下：

local cjson = require("cjson")local t = {["GET"] = {["/a"] = "f"}}function hehe(node)   node["TOKEN"] = node["TOKEN"] or {}   ngx.log(ngx.ERR, "0", cjson.encode(t["GET"]))   ngx.log(ngx.ERR, "0", cjson.encode(node))   ngx.log(ngx.ERR, "0", tostring(node))   node = node["TOKEN"]   ngx.log(ngx.ERR, "1", cjson.encode(t["GET"]))   ngx.log(ngx.ERR, "1", cjson.encode(node))   ngx.log(ngx.ERR, "1", tostring(node))   node["TOKEN"] = "123"   ngx.log(ngx.ERR, "2", cjson.encode(t["GET"]))   ngx.log(ngx.ERR, "2", cjson.encode(node))   ngx.log(ngx.ERR, "2", tostring(node))endhehe(t["GET"])ngx.say("ok")

nginx日志中的结果：

2017/07/10 15:28:16 [error] 20400#0: *749 [lua] access_by_lua(nginx.conf:138):8: hehe(): 0{"\/a":"f","TOKEN":{}}, client: 127.0.0.1, server: , request: "GET / HTTP/1.1", host: "127.0.0.1:8888"2017/07/10 15:28:16 [error] 20400#0: *749 [lua] access_by_lua(nginx.conf:138):9: hehe(): 0{"\/a":"f","TOKEN":{}}, client: 127.0.0.1, server: , request: "GET / HTTP/1.1", host: "127.0.0.1:8888"2017/07/10 15:28:16 [error] 20400#0: *749 [lua] access_by_lua(nginx.conf:138):10: hehe(): 0table: 0x41dfca60, client: 127.0.0.1, server: , request: "GET / HTTP/1.1", host: "127.0.0.1:8888"2017/07/10 15:28:16 [error] 20400#0: *749 [lua] access_by_lua(nginx.conf:138):13: hehe(): 1{"\/a":"f","TOKEN":{}}, client: 127.0.0.1, server: , request: "GET / HTTP/1.1", host: "127.0.0.1:8888"2017/07/10 15:28:16 [error] 20400#0: *749 [lua] access_by_lua(nginx.conf:138):14: hehe(): 1{}, client: 127.0.0.1, server: , request: "GET / HTTP/1.1", host: "127.0.0.1:8888"2017/07/10 15:28:16 [error] 20400#0: *749 [lua] access_by_lua(nginx.conf:138):15: hehe(): 1table: 0x41e011e0, client: 127.0.0.1, server: , request: "GET / HTTP/1.1", host: "127.0.0.1:8888"2017/07/10 15:28:16 [error] 20400#0: *749 [lua] access_by_lua(nginx.conf:138):18: hehe(): 2{"\/a":"f","TOKEN":{"TOKEN":"123"}}, client: 127.0.0.1, server: , request: "GET / HTTP/1.1", host: "127.0.0.1:8888"2017/07/10 15:28:16 [error] 20400#0: *749 [lua] access_by_lua(nginx.conf:138):19: hehe(): 2{"TOKEN":"123"}, client: 127.0.0.1, server: , request: "GET / HTTP/1.1", host: "127.0.0.1:8888"2017/07/10 15:28:16 [error] 20400#0: *749 [lua] access_by_lua(nginx.conf:138):20: hehe(): 2table: 0x41e011e0, client: 127.0.0.1, server: , request: "GET / HTTP/1.1", host: "127.0.0.1:8888"

结果分析：

1，lua中table相关操作包括做为function的参数都是引用操作，在function中对table node的key，value的相关操作都是对原table t的操作；

2，node = node["TOKEN"] 这一步操作相当于把node的内存地址指向了node["TOKEN"]的内存地址（即t["GET"]["TOKEN"]的内存地址），故之后对node的操作，都会影响到t["GET"]["TOKEN"]。