I don't completely understand setfenv

Help and Feedback Scripting Support
#1

Is there a way I can use setfenv while keeping the original environment at the same time?

#2

Sort of.

You can’t have both at once, but you can pass through failed indexes in your new environment to your old environment. You can do this using the __index metamethod, which handles what happens when you try to get a value from a table the doesn’t exist. Here’s an example:

local function passthroughEnv(func, newEnv)
	local oldEnv = getfenv(func)
	setmetatable(newEnv, {
		__index = function(self, index)
			return oldEnv[index]
		end
	})
	return setfenv(func, newEnv)
end

Any value already in newEnv is returned, but if it doesn’t exist in newEnv then __index is called, which will return the value from oldEnv.

Any new values you set will go into newEnv. You can control this with the __newindex metamethod if you need to.

Lua lets you do a little shortcut with the __index metamethod: you can set it directly to a table and it will just use that table’s members. Makes things lots easier!

Knowing this, we can write the following:

local function passthroughEnv(func, newEnv)
	local oldEnv = getfenv(func)
	setmetatable(newEnv, {
		__index = oldEnv
	})
	return setfenv(func, newEnv)
end

You can do other stuff with metatables. You should really learn them if you haven’t already!

Even though I’ve answered your question, I really wouldn’t advise messing with function environments unless it’s just for fun. It makes code harder to understand and maintain, and it messes up Roblox’s built-in helper checks.

11 Likes
Setfenv() and getfenv()
#3

I wrote my own script builder back when those were popular. Used metatables and setfenv to sandbox scripts made by the user.

I can’t really think of another use for setfenv besides script sandboxing, in any case. It is pretty interesting from a theoretical point of view, though.

#4

Thank you so much. I just am making an admin system and wanted to add a built in set of stuff for each command without having to pass it through a function.

1 Like