Scripting Helpers is winding down operations and is now read-only. More info→
Log in to vote
0
How do I set functions "off limits" in a customized environment?
Let's say that for whatever reason, I want to prevent myself from using the set/get metatable functions. I have no idea how to do this. Any help?
--Old environment here
excluded = {
setmetatable,
getmetatable
}
mt = {
__metatable = "Locked just in case.",
__index = getfenv()
}
setfenv(0, setmetatable({}, mt))
--New environment here
a = setmetatable({}, {}) --I don't want this to happen.
b = getmetatable(a) --Or this.
1 answer
Log in to vote
2
You'd want to set the function's environment to an empty table, with a metatable using __index to control what you can, and can't do. Which, you got close to, but not quite.
First, let's establish what we don't want anyone to access:
local Blocked = {
"getmetatable",
"setmetatable",
}
Now, let's make a function to check if an index is on our list:
function IsBlocked(tab, key)
-- Iterate the "tab" variable (should be a list)
for i,v in pairs(tab)do
-- if v is equal to the key we returned, then ...
if v==key then
-- return the key
return v
end
end
-- No match was found, return nil.
return nil
end
Set the new environment:
setfenv(1,setmetatable({},{
__index = function(t, key)
-- Get the blocked key
local keyBlocked = IsBlocked(Blocked, key)
-- if blocked key exists, then ...
if keyBlocked then
print("Error: "..keyBlocked.." is locked.")
-- return nil
return nil
else -- If not blocked ...
-- return old environment index
return getfenv()[key]
end
end
}))
Final product:
local Blocked = {
"getmetatable",
"setmetatable",
}
function IsBlocked(tab, key)
for i,v in pairs(tab)do
if v==key then
return v
end
end
return nil
end
setfenv(1,setmetatable({},{
__index = function(t, key)
local keyBlocked = IsBlocked(Blocked, key)
if keyBlocked then
print("Error: "..keyBlocked.." is locked.")
return nil
else
return getfenv()[key]
end
end,
__metatable = "no metatable for u",
}))
print(getmetatable) -- > Error: getmetatable is locked.
print(setmetatable) -- > Error: setmetatable is locked.
You can test it here as well: http://repl.it/BCua/1
