How to search in table member of another table in Lua

问题

I am writing a lua program that has a table which is a member of another table. When I add a new date to that member table everything is ok. But when I want to search in that table no matter what key I give I always get the last row added to the table. How do I search properly in that member table?

Stream = {name = ""}

function Stream:new(obj, name)
    obj = obj or {}
    setmetatable(obj, self)
    self.__index = self
    self.name = name or "default"
    --[[ declaration and initialization of another table memebers--]]
    return obj
end

Table = {streams = {}}

function Table:new(obj)
    obj = obj or {}
    setmetatable(obj, self)
    self.__index = self
    self.streams = {}
    --[[ declaration and initialization of another table memebers--]]
    return obj
end

table_ = Table:new(nil)

table_.streams["stdout"] = Stream:new(nil,"stdout")
table_.streams["stderr"] = Stream:new(nil,"stderr")

print("Stdout stream name:", table_.streams["stdout"].name)

print("Stream table content:")
for k, v in pairs(table_.streams) do
    print(k, v)
end

I expect the output to be: Stdout stream name: stdout

But I get: Stdout stream name: stderr

回答1:

I think you are misunderstanding what you should put in obj and what you should put in self in your :new functions. What you put in self ends up being shared between all objects you create via your :new function. You may want to look for more info on metatables. Here is small example to demonstrate

    local t = {}

    function t:new(name)
      local obj = {
        Name = name
      }
      setmetatable(obj, self)
      self.__index = self
      self.SharedName = name
      return obj
    end

    local o1 = t:new("a")
    print(o1.Name) -- a
    print(o1.SharedName) -- a

    local o2 = t:new("b")

    print(o1.Name) -- a
    print(o1.SharedName) -- b 

    -- after creating second object SharedName field was overwritten like in your case

    print(o2.Name) -- b
    print(o2.SharedName) -- b

来源：https://stackoverflow.com/questions/56111919/how-to-search-in-table-member-of-another-table-in-lua

标签

lua