Lua variable scoping with setfenv
I'm tr开发者_运维技巧ying to use raw Lua files for configuration purposes, but don't want the config files polluting the global namespace.
The problem I'm running into is that dofile
always seems to execute in the real global environment, so external files just throw all their declarations into _G.
Here's an example main file, with comments indicating my wishful thinking.
function myFunc()
print("In the sandbox:")
print("Should be 1:", a) -- falls back to _G for lookup
a = 2 -- instantiating new global for sandbox
print("Should be 2:", a) -- from sandbox
print("Should still be 1:", _G.a) -- from host environment
dofile("loading.lua") -- here's where things go wrong
print "\nBack in the sandbox:"
print("Should be 3:", a) -- changed by loadfile
print("Should STILL be 1:", _G.a) -- unchanged
end
a = 1
local newgt = {} -- new environment
setmetatable(newgt, {__index = _G})
setfenv(myFunc, newgt)
myFunc()
print("\nOutside of the sandbox:")
print("Should be 1: ", a) -- in theory, has never changed
And the file it's loading (loading.lua
:
print ("\nLoading file...")
print("Should be 2: ", a) -- coming from the sandbox environment
a = 3
print("Should be 3: ", a) -- made a change to the environment
And finally the output I'm seeing:
In the sandbox:
Should be 1: 1
Should be 2: 2
Should still be 1: 1
Loading file...
Should be 2: 1
Should be 3: 3
Back in the sandbox:
Should be 3: 2
Should STILL be 1: 3
Outside of the sandbox:
Should be 1: 3
The problem you describe is also discussed on this page Dofile Namespace Proposal. The solution seemed to be the following replacement for dofile
:
function myapp.import(name)
local f,e = loadfile(name)
if not f then error(e, 2) end
setfenv(f, getfenv(2))
return f()
end
See also: Sand Boxes
精彩评论