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  1. --[[
  2. lua readonly module
  3. 2013 (c) nyaocat
  4. this program is licensed under NYSL( http://w...content-available-to-author-only...s.net/nysl/ )
  5.  
  6. lua5.1 and lua5.2
  7. ]]
  8.  
  9. local newproxy = newproxy or require("newproxy")  -- for Lua5.2
  10. local type, getmetatable, pairs, assert, error = type, getmetatable, pairs, assert, error
  11. local next, ipairs, pairs = next, ipairs, pairs
  12.  
  13. local modname = ...
  14.  
  15. local readonly_table_tag = newproxy() -- unique tag
  16. local readonly = {}
  17.  
  18. function readonly.next(t, index )
  19.   local mt = getmetatable(t)
  20.   if mt and mt.__type == readonly_table_tag then
  21.     return getmetatable(t).__next(t, index )
  22.   else
  23.     return next(t, index)
  24.   end
  25. end
  26.  
  27. function readonly.pairs(t)
  28.   local mt = getmetatable(t)
  29.   if mt and mt.__type == readonly_table_tag then
  30.     return getmetatable(t).__next, t, nil
  31.   else
  32.     return pairs(t)
  33.   end
  34. end
  35.  
  36. local function iter(tbl, i)
  37.   i = i + 1
  38.   local var = tbl[i]
  39.   if var then
  40.     return i, var
  41.   end
  42. end
  43.  
  44. function readonly.ipairs(t)
  45.   local mt = getmetatable(t)
  46.   if mt and mt.__type == readonly_table_tag then
  47.     return iter, t, 0
  48.   else
  49.     return ipairs(t)
  50.   end
  51. end
  52.  
  53. function readonly.readonly(tbl)
  54.   assert(type(tbl) == "table" or type(tbl) == "userdata",
  55.          "Only user data or table is possible to read-only.")
  56.   local ret = newproxy(true)  -- ※
  57.   local mt = getmetatable(ret)
  58.   local tbl_mt = getmetatable(tbl)
  59.   if tbl_mt then
  60.     for k, v in pairs(tbl_mt) do
  61.       if k:match("^__") then
  62.         mt[k] = function(...) return v(...) end
  63.       end
  64.     end
  65.   end
  66.   mt.__len   = function() return #tbl end
  67.   mt.__index = function(ud, key) return tbl[key] end
  68.   mt.__newindex = function()
  69.     error("value of a read-only table can not be updated.")
  70.   end
  71.   mt.__type = readonly_table_tag
  72.   mt.__next   = function(t, index ) return next(tbl, index) end
  73.   return ret
  74. end
  75.  
  76. function readonly.readonly2(tbl) -- member function can be updated.
  77.   assert(type(tbl) == "table" or type(tbl) == "userdata",
  78.          "Only user data or table is possible to read-only.")
  79.   local ret = newproxy(true)
  80.   local mt = getmetatable(ret)
  81.   local tbl_mt = getmetatable(tbl)
  82.   if tbl_mt then
  83.     for k, v in pairs(tbl_mt) do
  84.       if k:match("^__") then
  85.         mt[k] = function(...) return v(...) end
  86.       end
  87.     end
  88.   end
  89.   mt.__len   = function() return #tbl end
  90.   mt.__index = function(ud, key)
  91.     if (type(tbl[key]) == "function") then
  92.       return function(self, ...) return tbl[key](tbl, ... ) end
  93.     else
  94.       return tbl[key]
  95.     end
  96.   end
  97.   mt.__newindex = function()
  98.     error("value of a read-only table can not be updated.")
  99.   end
  100.   mt.__type = readonly_table_tag
  101.   mt.__next   = function(t, index ) return next(tbl, index) end
  102.   return ret
  103. end
  104.  
  105. -- tests
  106.  
  107. if not (modname) then
  108.   local print, pcall = print, pcall
  109.   local ret, err = pcall(function()
  110.     arr = readonly.readonly {3, 9, 7, 4}
  111.     assert(pcall(function() local val = arr[2] end) == true )
  112.     assert(pcall(function() arr[1] = 98        end) == false)
  113.  
  114.     t1 = readonly.readonly {
  115.       val     = 10,
  116.       getVal  = function(self)         return self.val   end,
  117.       setVal  = function(self, newval) self.val = newval end
  118.     }
  119.     assert(pcall(function() t1:setVal(20) end) == false )
  120.     assert(pcall(function() t1:getVal()   end) == true  )
  121.     assert(pcall(function() t1.val = 30   end) == false )
  122.  
  123.     t2 = readonly.readonly2 {
  124.       val     = 10,
  125.       getVal  = function(self)         return self.val   end,
  126.       setVal  = function(self, newval) self.val = newval end
  127.     }
  128.     assert(pcall(function() t2:setVal(20) end) == true  )
  129.     assert(pcall(function() t2:getVal()   end) == true  )
  130.     assert(pcall(function() t2.val = 30   end) == false )
  131.   end)
  132.   if ret then
  133.     print("tests all ok")
  134.   else
  135.     print("test failed ...", err)
  136.   end
  137. end
  138.  
  139. return readonly
Success #stdin #stdout 0.02s 2496KB
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tests all ok
https://ideone.com/soulZG
language:
Lua (luac 5.3.3)
created:
10 years ago
visibility:
public

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