I'd like to re-initialize a table without losing references to it.
What I want to achieve is defining tables in files, and when a file is changed (with a text editor) the file is reloaded, changing the table. Of course this doesn't change the table but creates a new instance, old references will still point to the old table.
Any suggestions?
EDIT: I want to elaborate on what I want to achieve. An example with game characters and weapons. I want to modify the weapons.lua and so affect the characters.
-- weapons.lua
sword = { damage = 3 }
-- characters.lua
character = { weapon = sword }
Adding a level of indirection (putting "sword" inside "weapons") like suggested by JWT doesn't help, unless I split character into { weaponTable = weapons, weaponKey = "sword" } but I don't see this as an option.
Anchor everything that needs to survive in the global environment. Nesting is fine, and this doesn't have to be your primary reference. (You can still local things, but make sure to initialize those local variables from the global environment and update the global if you change the local.)
To initialize the global values, say
foo = foo or value -- if foo is always true-ish
bar = (bar == nil) and value or bar -- if bar may be `false`
To initialize or update tables, you can
foo = foo or { }
foo.bar = foo.bar or 23
foo.baz = foo.baz or 42
-- and so on...
but that's kinda icky, so maybe say
function reinit( new, old ) -- (re)initialize one level, prefer old
if old == nil then return new end
if type( old ) ~= "table" then return old end
for k, v in pairs( new ) do
if old[k] == nil then old[k] = v end
end
return old
end
function reset( new, old ) -- (re)initialize one level, prefer new
if old == nil then return new end
if type( old ) ~= "table" then return new end
for k, v in pairs( new ) do old[k] = v end
return old
end
and then just
foo = reinit( { bar = 23, baz = 42 }, foo ) -- only setting if not defined
-- or
foo = reset( { bar = 23, baz = 42 }, foo ) -- always overriding given fields
or maybe make it even more fancy and say
function traverse( t, path )
local here, last, lastk, created = t
-- follow path of several keys starting from t, creating tables as needed
for k in path:gmatch "[^.]+" do
k = tonumber( k ) or k -- convert all-number keys to integer (for arrays)
local next = here[k]
if not next then
next, created = { }, true
here[k] = next
else
created = false
end
lastk, last, here = k, here, next
end
return here, last, lastk, created
end
function repopulate( path, value, update )
update = update or reinit -- pass 'reset' as 'update' for the other behavior
-- or something entirely different if that's what you need
local here, last, lastk, created = traverse( _G, path )
if type( value ) == "table" then
update( value, here )
else
if created then last[lastk] = nil end -- created one level too much
update( { [lastk] = value }, last )
end
end
and then (with arbitrary nesting)
-- No need to create 'state' first if it doesn't exist yet!
-- (If it exists, it will get updated, otherwise it's created)
repopulate( "state.player.weapon", { kind = "sword", damage = 11 } )
-- Do keep in mind that generally update order is relevant -- you may want to
-- give a newly created player a default inventory, but you may not want to
-- "refill" the player's inventory on every reload. So generally `repopulate`
-- with the parent and all child nodes for from-scratch creation, then
-- `repopulate` the child nodes that need to be checked & potentially updated
-- as well.
-- (So here you'd probably repopulate `state.player` first and then
-- `state.player.weapon` or other fields only if they should be updated anyway.)
-- e.g.:
repopulate( "state.player", {
x = 0, y = 0, hp = 100, mp = 100, level = 0, -- and so on
weapon = { kind = "sword", damage = 11 }, -- etc. etc.
} )
-- on reload always force a sword-kind weapon, leave rest (damage, ...) as-is
repopulate( "state.player.weapon", { kind = "sword" }, reset )
-- or alternatively: only if player has no weapon, give them a sword
repopulate( "state.player.weapon", { kind = "sword", damage = 3 } )
And you can go further, add metamethods to hide some of that shuffling, define different update policies, ... – you've seen some of the possibilities, now go and build your own version that fits your style and your code.
(While you're free to use the above code in any way, please note that it was written ad-hoc in the browser. I did some testing, fixed some glitches, and it seems to work now, but don't be surprised if there's still one or two bugs hiding in there. So play with this, change it, break it (and see how/why it breaks), adapt and extend it, ... – but unless you completely understand what it does and can fix any bugs, I strongly suggest you write your own version, or just stick to the basics. You probably don't need everything that this does, and you're likely to need other things that this doesn't do. As this is a central part of the reloading/live-coding infrastructure and everything has to be adapted to be reload-compatible, any mismatch between your tooling and what you actually need will result in a lot of pain everywhere in your code. So if you need something like this, put in a day or two to make it work the way you need it to, or you will regret it.)
(Free bonus warning: If you do OOP, you'll probably have to store and retrieve your classes instead of creating them every time, otherwise old objects from previous iterations will miss code updates and still run their old methods. I've forgotten about that more than just a couple of times and wasted several hours pondering "why isn't it fixed now?!?" after repeatedly re-loading code... So remember to anchor your metatables, anchor your classes!)
You could nest the tables in another table.
Before:
local a = { 1, 2, 3 }
local b = { 7, 8, 9 }
print(a[2] + b[2]) -- #=> 10
After:
local lookup = {
a = { 1, 2, 3 },
b = { 7, 8, 9 }
}
print(lookup.a[2] + lookup.b[2]) -- #=> 10
Then you can fully replace (or just update) a table in the lookup table and any dependent statements will use that updated value:
lookup.a = { 100, 50, 0 }
print(lookup.a[2] + lookup.b[2]) -- #=> 58
I don't know if it's exactly what you needed (As an ID is necessary) but I hope it will fit your needs.
meta = {
tables = {},
__call = function(arg, t)
for k, v in pairs(t) do
arg[k] = v
end
end,
__bnot = function(arg)
return arg.__key
end,
__newindex = function(arg, key, val)
meta.tables[arg.__key][key] = val
end,
__index = function(arg, key)
return meta.tables[arg.__key][key]
end
}
function RefTable(arg)
local newtable = {}
if arg ~= nil then
newtable.__key = arg
setmetatable(newtable, meta)
if meta.tables[arg] == nil then
meta.tables[arg] = {}
end
else
error("RefTable can't have nil key")
end
return newtable
end
-- Using the RefTable
sword = RefTable("Sword")
sword({damage = 3})
sword.cooldown = 10
character = {sword = sword}
print("base", sword.damage, sword.cooldown)
print("embed", character.sword.damage, character.sword.cooldown)
sword = RefTable("Sword")
sword({damage = 8, cooldown = 50})
print("embed2", character.sword.damage, character.sword.cooldown)
print(sword.__key, sword.cooldown)
ref = RefTable("Sword")
ref.cooldown = 1000
print(sword.cooldown)
Related
Edited for more details:
I'm trying to have a turtle that is sitting in front of a sapling wait for it to grow before cutting it down. It compares the log to the item in front until it matches. The system I'm currently using works, but I was hoping there was a slightly more minimal way to write it.
checkTarget = {
forward = function(tgt)
check = {turtle.inspect()} --creates table with first as boolean, second as information table
local rtn = {false, check[2]}
if type(tgt) == "table" then
for k, v in pairs(tgt) do
if check[2].name == v then
rtn = {true, v}
break
end
end
elseif tgt == nil then
return check[1]
elseif check[2].name == tgt then
rtn[1] = true
end
return rtn
end,--continued
This takes an argument, either a string or an array of strings, to compare against. When it checks the block in front it saves the detailed information to the second element in rtn and the first to a default of false. If the string matches the checked block's name, then it changes rtn[1] to true and returns all of it, which is the table at the bottom when doing checkTarget.forward("minecraft:log").
My question was, I am currently making a disposable variable to store the array that is returned from checkTarget, and then calling the variable's first element to get if it's true or not. I was hoping there was a way to include it in the if statement without the disposable variable (tempV)
repeat
local tempV = fox.checkTarget.forward("minecraft:log")
if tempV[1] then
cut()
fox.goTo({x = 0, y = 0, z = 0})
fox.face(0)
end
tempV = fox.checkTarget.forward("minecraft:log")
until not run
{
false,
{
state = {
stage = 0,
type = "birch",
},
name = "minecraft:sapling",
metadata = 2
}
}
Instead of
local tempV = fox.checkTarget.forward("minecraft:log")
if tempV[1] then
end
You can do
if fox.checkTarget.forward("minecraft:log")[1] then
end
and then calling the variable's first element to get if it's true or
not.
With tempV[1] you're not calling the first element, you're indexing it.
To call something you have to use the call operator () which doesn't make sense as a boolean is not callable.
I'm currently starting work on a text adventure game in Lua--no addons, just pure Lua for my first project. In essence, here is my problem; I'm trying to find out how I can do a "reverse lookup" of a table using one of its variables. Here's an example of what I've tried to do:
print("What are you trying to take?")
bag = {}
gold = {name="Gold",ap=3}
x = io.read("*l")
if x == "Gold" then
table.insert(bag,gold)
print("You took the " .. gold.name .. ".")
end
Obviously, writing a line like this with every single object in the game would be very... exhausting--especially since I think I'll be able to use this solution for not just taking items but movement from room to room using a reverse lookup with each room's (x,y) coordinates. Anyone have any ideas on how to make a more flexible system that can find a table by the player typing in one of its variables? Thanks in advance!
-blockchainporter
This doesn't directly answer your question as you asked it, but I think it would serve the purpose of what you are trying to do. I create a table called 'loot' which can hold many objects, and the player can place any of these in their 'bag' by typing the name.
bag = {}
loot = {
{name="Gold", qty=3},
{name="Axe", qty=1},
}
print("What are you trying to take?")
x = io.read("*l")
i = 1
while loot[i] do
if (x == loot[i].name) then
table.insert(bag, table.remove(loot,i))
else
i = i + 1
end
end
For bonus points, you could check 'bag' to see if the player has some of that item already and then just update the quantity...
while loot[i] do
if (x == loot[i].name) then
j, found = 1, nil
while bag[j] do
if (x == bag[j].name) then
found = true
bag[j].qty = bag[j].qty + loot[i].qty
table.remove(loot,i)
end
j = j + 1
end
if (not found) then
table.insert(bag, table.remove(loot,i))
end
else
i = i + 1
end
end
Again, this isn't a 'reverse lookup' solution like you asked for... but I think it is closer to what you are trying to do by letting a user choose to loot something.
My disclaimer is that I don't use IO functions in my own lua usage, so I have to assume that your x = io.read("*l") is correct.
PS. If you only ever want objects to have a name and qty, and never any other properties (like condition, enchantment, or whatever) then you could also simplify my solution by using key/val pairs:
bag = {}
loot = { ["Gold"] = 3, ["Axe"] = 1 }
print("What are you trying to take?")
x = io.read("*l")
for name, qty in pairs(loot) do
if x == name then
bag.name = (bag.name or 0) + qty
loot.name = nil
end
end
I have a few notes to start before I specifically address your question. (I just want to do this before I forget, so please bear with me!)
I recommend printing to the terminal using stderr instead of stdout--the Lua function print uses the latter. When I am writing a Lua script, I often create a C-style function called eprintf to print formatted output to stderr. I implement it like this:
local function eprintf(fmt, ...)
io.stderr:write(string.format(fmt, ...))
return
end
Just be aware that, unlike print, this function does not automatically append a newline character to the output string; to do so, remember to put \n at the end of your fmt string.
Next, it may be useful to define a helper function that calls io.read("*l") to get an entire line of input. In writing some example code to help answer your question, I called my function getline--like the C++ function that has similar behavior--and defined it like this:
local function getline()
local read = tostring(io.read("*l"))
return read
end
If I correctly understand what it is you are trying to do, the player will have an inventory--which you have called bag--and he can put items into it by entering item names into stdin. So, for instance, if the player found a treasure chest with gold, a sword, and a potion in it and he wanted to take the gold, he would type Gold into stdin and it would be placed in his inventory.
Based on what you have so far, it looks like you are using Lua tables to create these items: each table has a name index and another called ap; and, if a player's text input matches an item's name, the player picks that up item.
I would recommend creating an Item class, which you could abstract nicely by placing it in its own script and then loading it as needed with require. This is a very basic Item class module I wrote:
----------------
-- Item class --
----------------
local Item = {__name = "Item"}
Item.__metatable = "metatable"
Item.__index = Item
-- __newindex metamethod.
function Item.__newindex(self, k, v)
local err = string.format(
"type `Item` does not have member `%s`",
tostring(k)
)
return error(err, 2)
end
-- Item constructor
function Item.new(name_in, ap_in)
assert((name_in ~= nil) and (ap_in ~= nil))
local self = {
name = name_in,
ap = ap_in
}
return setmetatable(self, Item)
end
return Item
From there, I wrote a main driver to encapsulate some of the behavior you described in your question. (Yes, I know my Lua code looks more like C.)
#!/usr/bin/lua
-------------
-- Modules --
-------------
local Item = assert(require("Item"))
local function eprintf(fmt, ...)
io.stderr:write(string.format(fmt, ...))
return
end
local function printf(fmt, ...)
io.stdout:write(string.format(fmt, ...))
return
end
local function getline()
local read = tostring(io.read("*l"))
return read
end
local function main(argc, argv)
local gold = Item.new("Gold", 3)
printf("gold.name = %s\ngold.ap = %i\n", gold.name, gold.ap)
return 0
end
main(#arg, arg)
Now, as for the reverse search which you described, at this point all you should have to do is check the user's input against an Item's name. Here it is in the main function:
local function main(argc, argv)
local gold = Item.new("Gold", 3)
local bag = {}
eprintf("What are you trying to take? ")
local input = getline()
if (input == gold.name) then
table.insert(bag, gold)
eprintf("You took the %s.\n", gold.name)
else
eprintf("Unrecognized item `%s`.\n", input)
end
return 0
end
I hope this helps!
Sorry in advance if this is an incorrect question. I'm fairly new to Lua and I'm not sure how to go about this. I want to access a variable stored in a table from a function variable.
As far as I know there is no self-referencing tables before constructed.
An example would be this:
local bigTable = {
a = {
foo = 0,
bar = function(y)
print(foo) --Incorrect
end
}
}
What would be the best approach for this situation?
What you want to do is to create a table first, and append the keys to it:
local a = {}
a.foo = 0
a.bar = function()
print(a.foo)
end
local bigTable = {
a = a
}
bigTable.a.bar() -- prints 0
local bigTable = {
a = {
foo = 0,
bar = function(self, ...)
print(self.foo)
end,
}
}
-- Somewhere else in the code...
bigTable.a.bar(bigTable.a) --> 0
-- or the shorter but (almost) equivalent form:
bigTable.a:bar() --> prints 0
I anticipate your next question will be "What does the : do?", and for that there's lots of answers on SO already :)
Note that there's potential for a performance improvement here: if the above code gets called a lot, the bar method will be created again and again, so it could make sense to cache it; but that's pointless unless the surrounding code is already fast enough that this one allocation would have a noticeable impact on its runtime.
No matter how I approach Lua, I run into this error all the time, so I must not understand something inherit to the language:
attempt to call method 'func' (a nil value)
I've seen the error here a few times as well but the problem doesn't seem clear to me.
Here's my module:
actor.lua
Actor = {
x = 0,
mt = {},
new = function()
local new_actor = {}
new_actor.x = Actor.x
new_actor.mt = Actor.mt
return new_actor
end,
test = function(self, a, b)
print(a, b)
end
}
I'm using Löve.
main.lua
require "game/actor"
local a = Actor:new() --works fine
function love.load()
a.x = 10
print(a.x) --output: 10
a:test(11, 12) --error: attempt to call method 'test' (a nil value)
end
I'm also not sure when it's appropriate to use the previous styling over this in a module.
Actor = {
x = 0
}
Actor.mt = {}
function Actor.new()
print(42)
end
I'm honestly not sure what is more correct than the other but considering I run into a simple error either way, there's probably something I'm missing entirely?
It looks like you're trying to instance a kind of class made of metatables. You basically need to assign new_actor's metatable with Actor.mt. (Resuming the problem: when you're indexing new_actor you're not indexing Actor in this case)
setmetatable(new_actor, Actor.mt);
Even if the metatable is being added, it won't work until you put the meta "__index" event to index a table containing your class methods/values, in this case:
Actor.mt = {
__index = Actor
};
I'd suggest moving your class methods/values into a new table, like Actor.prototype, Actor.fn, etc... avoiding conflicts:
Actor.fn = {
test = function(self, a, b)
print(a, b)
end
};
Actor.mt = {
__index = Actor.fn
};
More about metatables in Lua 5.3 manual.
How can I get variables that not declared yet?
Here are simple example:
a = b
b = 123
What I want from these 2 lines is a << 123. But obv it doesn't work.
I know the easy way to get the answer a = 123 is cut 1st line and paste it to lower than 2nd line.
But I'm in some problem. I need some function like 'WillDeclaredVar()' that I can use in like this:
a = WillDeclaredVar(b)
sheepCount = 123
b = sheepCount
print(a)
so I can get the answer '123'.
Or there are any built-in functions that will allows me to do similar thing?
===
I think the link given by timrau is not telling my case. the key point is how to get Variables 'that not declared yet'.
===
Adding actual Code:
triggerCount = 0 -- Counting number of 'Trigger' function
local Trigger = function (t)
triggerCount = triggerCount + 1
return Trigger (t)
end
-- following Triggers are same as while statement.
-- following Triggers doing: Add 1 MarineCount until get 64000 MarineCount
Trigger { -- Here the Trigger function. Now triggerCount = 1.
players = {P1}
actions = {
SetDeaths(P1, Add, 1, "Terran Marine")
},
flag = {preserved},
}
Portal(LoopStart);
-- function Portal(VariableName) returns VariableName = triggerCount. So LoopStart = 1.
Trigger { -- Now triggerCount = 2.
players = {P1}
actions = {
LinkList(LoopEnd, LoopStart);
-- function LinkList(From, To) changes 'From' Trigger's next pointer to the 'To' Trigger.
-- But now the problem happens. Because 'LoopEnd' is not declared yet.
},
flag = {preserved},
}
Trigger { -- Now triggerCount = 3.
players = {P1}
conditions = {
Deaths(P1, Exactly, 64000, "Terran Marine");
}
actions = {
_LinkList(LoopEnd);
-- Reset LoopEnd's next pointer(= LoopEscape) if MarineCount hits 64000
},
flag = {preserved},
}
Portal(LoopEnd); -- LoopEnd = 3.
Changing Order of Triggers will break the Trigger logic(while statement).
All i want is get easy to coding. To put in bluntly, I don't need to solve this problem(get undeclared var). I can imagine a few ways to avoid it. But if i using these ways then the coding work will be very complicated and the difficulty of coding will increases greatly. The difficulty made me stop coding in recent months.
How can I get variables that not declared yet?
Short of time travel, you can't.
Your example code doesn't explain the motivation for the question, because this:
a = WillDeclaredVar(b)
sheepCount = 123
b = sheepCount
print(a)
Can trivially be rearranged into this:
sheepCount = 123
b = sheepCount
a = WillDeclaredVar(b)
print(a)
It would be easier to answer your question if you showed the actual problem you're trying to solve (to avoid an XY problem).
However, as stated there are few things we can note.
First, you need to distinguish between declaring a variable and giving it a value. In Lua you can say:
local b
To declare b as a local variable, which presumably will make a slot for it in the stack frame and let you bind closures to it, before you give it a value. However, the line:
a = WillDeclaredVar(b)
Will pass WillDeclaredVar the value that b currently has, and there's no way for a to change retroactively as a result of b being assigned a new value. That's simply not going to happen, ever. Neither a nor WillDeclaredVar are even aware that b exists, they are receive the value it contains at the point of call.
You could however bind the variable b to a closure which will fetch b's current value when needed.
-- declare b before giving it a value, aka "forward reference"
local b
a = function() return b end
sheepCount = 123
b = sheepCount
print(a()) -- call a to get b's current value
Another way to do that would be to make b a global variable, which is really just a key into your environment table, so you could say:
a = WillDeclaredVar('b')
And have a be some object that can fetch the current value of __ENV['b'] when required.
However, neither of these will support this syntax:
print(a)
a needs to be a function, something that looks up the value of b when needed rather than simply holding a previously computed value. You could do it in this particular instance (i.e. a needs to be convertable to a string), by creating a proxy object that implements __tostring.
function WillDeclaredVar(variableName)
local proxy = { environment = _ENV or _G, variableName = variableName }
return setmetatable(proxy, {
__tostring = function(proxy)
return proxy.environment[proxy.variableName]
end
})
end
-- a will compute a value based on the current value of b when needed
a = WillDeclaredVar('b')
sheepCount = 123
b = sheepCount
print(a)
Output:
123
To make var1 be a reference for var2 write var1 = ReferenceF or var2 (please note a space inside "ReferenceFor"!)
do
local values, references, reference_flag = {}, {}
setmetatable(_G, {
__index = function (_, name)
if name == 'ReferenceF' then
reference_flag = true
elseif reference_flag then
reference_flag = false
return {[references] = name}
elseif references[name] then
return _G[references[name]]
else
return values[name]
end
end,
__newindex = function (_, name, val)
if type(val) == 'table' and val[references] then
references[name] = val[references]
else
values[name] = val
end
end
})
end
a = ReferenceF or b -- a is Reference For b
b = ReferenceF or c -- b is Reference For c
sheepCount = 123
c = sheepCount
print(a, b, c) --> 123 123 123