173 posts
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The hall of 1000 monkeys and only 1 typewriter
Posted 08 October 2016 - 01:37 PM
Simple question. Where are local variables stored?
I'm fairly sure global variables, tables and functions are stored in _G but I'm not sure where to find local variables. There's no particular reason to this, I was just curious
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Posted 08 October 2016 - 01:42 PM
Under LuaJ (the implementation which ComputerCraft uses) when each function gets called it allocates an array of
LuaValues to represent a local variable. When you do:
local a, b = 1, 2
return a + b
It will store 1 in slot 0, 2 in slot 1 and then get slots 0 and 1 and add them together.
You can Cobalt's implementation of the VM
here which is mostly the same as LuaJ's: note the
stack variable: this stores all the locals.
Edited on 08 October 2016 - 11:42 AM
173 posts
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The hall of 1000 monkeys and only 1 typewriter
Posted 08 October 2016 - 01:50 PM
Oh ok, I'd assume we can't access stack in-game
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Tasmania (AU)
Posted 08 October 2016 - 02:38 PM
I'd assume not; certainly there's no accessible equivalent in regular Lua.
Furthermore, within ComputerCraft at least, globals you declare aren't going into _G. The bios script each system runs on boot starts the shell with a unique environment table, and all globals go into there. The shell and multishell scripts load their APIs into the current global environment, which means you can't find those through _G for example - this is why other APIs can't access shell / multishell (because they don't get access to any specific shell's environment table).
If you want the current environment table, getfenv() can return it to you.
173 posts
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The hall of 1000 monkeys and only 1 typewriter
Posted 08 October 2016 - 03:19 PM
oh cool. How would I use getfenv()? I tried using it in the lua prompt but I kept being returned with table: 68953f
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Does anyone put something serious here?
Posted 08 October 2016 - 03:27 PM
Oh ok, I'd assume we can't access stack in-game
Shameless plug: If you have
CCTweaks installed then you can add the
debug library which allows direct access to the stack and upvalues.
oh cool. How would I use getfenv()? I tried using it in the lua prompt but I kept being returned with table: 68953f
That table is the environment just CC's pretty printing functions don't handle it. You can use it like any other table:
local env = getfenv()
assert(env == _ENV)
assert(env.print == print)
for k, v in pairs(env) do print(k, v) end
It is worth noting that in later versions you should use
_ENV rather than
getfenv() as the latter is being phased out. You may note when iterating over the environment that it doesn't have any members: this is because it uses
metatables to lookup in the parent environment if it can't find it in this one: try
getmetatable(_ENV).__index.
173 posts
Location
The hall of 1000 monkeys and only 1 typewriter
Posted 08 October 2016 - 05:04 PM
okie! Ta :)/>