垃圾收集器在收集死對象時會做什麼？

Question

請按照我的意見輸入（使用Lua 5.3.2在JDoodle）：

local table = {}; 

local weakvalues = setmetatable(
{ 
    table 
}, 
{ 
    -- Let weakvalues values 
    -- be weak, so that they fade when dead objects are g-c. 
    __mode = 'v' 
}); 

table = _; 

-- Now the previously ref. table is unreachable 
-- since there are no other references, I think so... 

-- Sychronously wait this loop statements 
-- in order to execute a next statement (maybe the 
-- garbage-collector would have collected the unreachable table above 
-- while this loop executes). 
for i = 1, 5e7 do end 

-- Expected to log 0, but it logs 1. Is the unreachable table 
-- still reachable? 
print(#weakvalues); 

我想表在table與nil分配table後會刪除weakvalues[1]。

Answer 1

您的代碼不會收集垃圾。 試試這個代碼

local t = {} 
local weakvalues = setmetatable({t},{ __mode = 'v'}) 
t = nil 
collectgarbage() collectgarbage() 
print(#weakvalues);