require 'class'
Paddle=class{}
function Paddle:init(x,y,width,height)
self.x=x
self.y=y
self.width=width
self.height=height
self.dy=0
end function Paddle:update(dt)
if self.dy < 0 then
self.y = math.max(`enter code here`0, self.y + self.dy * dt)
else
self.y=math.min(VIRTUAL_HEIGHT,-self.height,self.y+self.dy*dt)
end
end
function Paddle:render()
love.graphics.rectangle('fill',self.x,self.y,self.width,self.height)
end
I am following the course CS50 lecture 0 pong update 5, and the same code is working for the teacher. I don't know why this is happening neither understand the problem because it makes no sense. If you want, here's 'class'. This problem isn't happening in the other class I made called 'ball' which does exactly the same thing. I also defined self.dy, and it does have a value "0" so I don't know why it does that error and what that error means.
local function include_helper(to, from, seen)
if from == nil then
return to
elseif type(from) ~= 'table' then
return from
elseif seen[from] then
return seen[from]
end
seen[from] = to
for k,v in pairs(from) do
k = include_helper({}, k, seen) -- keys might also be tables
if to[k] == nil then
to[k] = include_helper({}, v, seen)
end
end
return to
end
-- deeply copies `other' into `class'. keys in `other' that are already
-- defined in `class' are omitted
local function include(class, other)
return include_helper(class, other, {})
end
-- returns a deep copy of `other'
local function clone(other)
return setmetatable(include({}, other), getmetatable(other))
end
local function new(class)
-- mixins
class = class or {} -- class can be nil
local inc = class.__includes or {}
if getmetatable(inc) then inc = {inc} end
for _, other in ipairs(inc) do
if type(other) == "string" then
other = _G[other]
end
include(class, other)
end
-- class implementation
class.__index = class
class.init = class.init or class[1] or function() end
class.include = class.include or include
class.clone = class.clone or clone
-- constructor call
return setmetatable(class, {__call = function(c, ...)
local o = setmetatable({}, c)
o:init(...)
return o
end})
end
-- interface for cross class-system compatibility (see https://github.com/bartbes/Class-Commons).
if class_commons ~= false and not common then
common = {}
function common.class(name, prototype, parent)
return new{__includes = {prototype, parent}}
end
function common.instance(class, ...)
return class(...)
end
end
-- the module
return setmetatable({new = new, include = include, clone = clone},
{__call = function(_,...) return new(...) end})
So this is the part where I call the update function, which is what someone said might be the error
function love.update(dt)
if love.keyboard.isDown('w') then
player1.dy=-PADDLE_SPEED
elseif love.keyboard.isDown('s') then
player1.dy=PADDLE_SPEED
else
player1.dy=0
end
if love.keyboard.isDown('up') then
player2.dy=-PADDLE_SPEED
elseif love.keyboard.isDown('down') then
player2.dy=PADDLE_SPEED
else
player2.dy=0
end
if gameState=='play' then
ball.update(dt)
end
player1.update(dt)
player2.update(dt)
This error is pretty clear on what you're doing wrong.
You're indexing local self, a number value.
That means that somewhere you're doing something like self.dy where self is not a table but a number and using the index operator . on numbers is not allowed as it does not make any sense.
The question is why self is not a table.
function myTable:myFunction() end
is short (syntactic sugar) for
function myTable.myFunction(self) end
and the function call
myTable:myFunction() is short for myTable.myFunction(myTable)
Please refer to the Lua manual.
Function Calls
Function Definitions
Find a function in your code that is defined with : and called with . and gets a number as first argument during that call.
That way a number ends up where you expect self.
I guess the error is in the main.lua which you did not provide.
There you have several calls to Paddle:update(dt). Writing myPaddle.update(dt) would cause that error for example. But I can't tell for sure as you did not provide your code.
But that it works for the teacher, but not for you is usually because you do something different/wrong.
Edit:
As you've provided more code I can tell for sure that the observed error is caused by
ball.update(dt)
player1.update(dt)
player2.update(dt)
This will put dt a number value, where the function expects self, the table ball.
replace it by
ball.update(ball, dt) or ball:update(dt)
player1.update(player1, dt) or player1:update(dt)
player2.update(player2, dt) or player2:update(dt)
I want to have a read only table in my Lua program. If ever a key is removed or a key is associated with a new value, an error must be thrown.
function readonly(table)
local meta = { } -- metatable for proxy
local proxy = { } -- this table is always empty
meta.__index = table -- refer to table for lookups
meta.__newindex = function(t, key, value)
error("You cannot make any changes to this table!")
end
setmetatable(proxy, meta)
return proxy -- user will use proxy instead
end
It works great.
t = { }
t["Apple"] = "Red"
t[true] = "True!"
t[51] = 29
for k,v in pairs(t) do
print(v)
end
t = readonly(t)
t[51] = 30
Prints
Red
True!
29
input:7: You cannot make any changes to this table!
Problem
for k, v in pairs(t) do
print(v)
end
Will print nothing under all circumstances now. That's because the proxy table will never have anything inside of it. pairs apparently never calls index and thus cannot retrieve anything from the actual table.
What can I do to make this readonly table iterable?
I'm on Lua 5.1 and have access to these metamethods:
Lua 5.1 Manual
You can modify standard Lua function pairs to work correctly with your read-only tables.
local function readonly_newindex(t, key, value)
error("You cannot make any changes to this table!")
end
function readonly(tbl)
return
setmetatable({}, {
__index = tbl,
__newindex = readonly_newindex
})
end
local original_pairs = pairs
function pairs(tbl)
if next(tbl) == nil then
local mt = getmetatable(tbl)
if mt and mt.__newindex == readonly_newindex then
tbl = mt.__index
end
end
return original_pairs(tbl)
end
Usage:
t = { }
t["Apple"] = "Red"
t[true] = "True!"
t[51] = 29
for k,v in pairs(t) do
print(k, v)
end
t = readonly(t)
for k,v in pairs(t) do
print(k, v)
end
t[51] = 30
One solution is to create a wholly custom iterator for the table.
function readonly(table)
local meta = { } -- metatable for proxy
local proxy = { } -- this table is always empty
meta.__index = table -- refer to table for lookups
meta.__newindex = function(t, key, value)
error("You cannot make any changes to this table!")
end
local function iter()
return next, table
end
setmetatable(proxy, meta)
return proxy, iter -- user will use proxy instead
end
Usage:
t = { }
t["Apple"] = "Red"
t[true] = "True!"
t[51] = 29
for k,v in pairs(t) do
print(v)
end
t, tIter = readonly(t)
t[51] = 30
for k, v in tIter do
print(v)
end
I am trying to convert existing python function into lua function. But my lua function is not producing same result as python function. Any help is appreciated.
Python function:
import json
test = '{"http://localhost:8080/":{"phone":{"-detail/phone detail.template.html":"5167n,a,7,2","s/motorola-xoom-with-wifi.json":"516a0,5,4,3"},"favicon.ico":"016ad,3,3,2","img/phones/motorola-xoom-with-wi-fi.":{"1.jpg":"*02s,2s,4v,h3|116da,o,l,6","2.jpg":"*02s,2s,4v,kp|116da,j,i,8","3.jpg":"*02s,2s,4v,ob|116da,o,m,8,7,,7,7,7","4.jpg":"*02s,2s,4v,rx|116da,o,m,9,8,,7,7,7","5.jpg":"*02s,2s,4v,vj|116da,p,m,a,8,,7,7,7"}}}'
def tri(param):
t = {}
for key in param:
if key not in param:
continue
if isinstance(param[key], dict) and param[key] is not None:
flat = tri(param[key])
for x in flat:
if x not in flat:
continue
t[key + x] = flat[x]
else:
t[key] = param[key]
return t
print(tri(json.loads(test)))
Lua code ( which is not producing same result as python function)
local json = require('cjson')
local test = '{"http://localhost:8080/":{"phone":{"-detail/phone-detail.template.html":"5167n,a,7,2","s/motorola-xoom-with-wi-fi.json":"516a0,5,4,3"},"favicon.ico":"016ad,3,3,2","img/phones/motorola-xoom-with-wi-fi.":{"1.jpg":"*02s,2s,4v,h3|116da,o,l,6","2.jpg":"*02s,2s,4v,kp|116da,j,i,8","3.jpg":"*02s,2s,4v,ob|116da,o,m,8,7,,7,7,7","4.jpg":"*02s,2s,4v,rx|116da,o,m,9,8,,7,7,7","5.jpg":"*02s,2s,4v,vj|116da,p,m,a,8,,7,7,7"}}}'
local function tri(param)
t = {}
for key in pairs(param) do
if param[key] == nil then end
if type(param[key]) == "table" then
flat = tri(param[key])
for k in pairs(flat) do
t[key .. k] = flat[k]
end
else
t[key] = param[key]
end
end
return t
end
print(json.encode(tri(json.decode(test))))
local function tri(param)
t = {} -- every time we call tri t will be "reset" to an empty table
for key in pairs(param) do
if param[key] == nil then end
if type(param[key]) == "table" then
flat = tri(param[key]) -- here we call tri, but we still need t!
for k in pairs(flat) do
t[key .. k] = flat[k]
end
else
t[key] = param[key]
end
end
return t
end
Making at least t global should solve that problem. But there is also no reason for flat to be global so we make it local too.
local function tri(param)
local t = {}
for key in pairs(param) do
if param[key] == nil then end
if type(param[key]) == "table" then
local flat = tri(param[key])
for k in pairs(flat) do
t[key .. k] = flat[k]
end
else
t[key] = param[key]
end
end
return t
end
Your task could be done a bit easier using json.traverse() function from this Lua JSON module.
Traversing lets you perform arbitrary operations with JSON elements on-the-fly.
This code concatenates element's path (for every JSON element except JSON containers: arrays/objects) and uses it as a key for Lua table.
local json = require'json'
local t = {}
local function callback(path, json_type, value)
if value ~= nil then -- value == nil for containers (arrays/objects)
t[table.concat(path)] = value
end
end
local test = '{"http://localhost:8080/":{"phone":{"-detail/phone detail.template.html":"5167n,a,7,2","s/motorola-xoom-with-wifi.json":"516a0,5,4,3"},"favicon.ico":"016ad,3,3,2","img/phones/motorola-xoom-with-wi-fi.":{"1.jpg":"*02s,2s,4v,h3|116da,o,l,6","2.jpg":"*02s,2s,4v,kp|116da,j,i,8","3.jpg":"*02s,2s,4v,ob|116da,o,m,8,7,,7,7,7","4.jpg":"*02s,2s,4v,rx|116da,o,m,9,8,,7,7,7","5.jpg":"*02s,2s,4v,vj|116da,p,m,a,8,,7,7,7"}}}'
json.traverse(test, callback)
-- Now t == {
-- ["http://localhost:8080/favicon.ico"] = "016ad,3,3,2",
-- ["http://localhost:8080/img/phones/motorola-xoom-with-wi-fi.1.jpg"] = "*02s,2s,4v,h3|116da,o,l,6",
-- ["http://localhost:8080/img/phones/motorola-xoom-with-wi-fi.2.jpg"] = "*02s,2s,4v,kp|116da,j,i,8",
-- ["http://localhost:8080/img/phones/motorola-xoom-with-wi-fi.3.jpg"] = "*02s,2s,4v,ob|116da,o,m,8,7,,7,7,7",
-- ["http://localhost:8080/img/phones/motorola-xoom-with-wi-fi.4.jpg"] = "*02s,2s,4v,rx|116da,o,m,9,8,,7,7,7",
-- ["http://localhost:8080/img/phones/motorola-xoom-with-wi-fi.5.jpg"] = "*02s,2s,4v,vj|116da,p,m,a,8,,7,7,7",
-- ["http://localhost:8080/phone-detail/phone detail.template.html"] = "5167n,a,7,2",
-- ["http://localhost:8080/phones/motorola-xoom-with-wifi.json"] = "516a0,5,4,3"
-- }
I am trying to build an elegant transpose function using functions mapn and zip in Lua.
The mapn and zip are as follows (From the lua book):
function map(func, array)
local new_array = {}
for i,v in ipairs(array) do
new_array[i] = func(v)
end
return new_array
end
function mapn(func, ...)
local new_array = {}
local i=1
local arg_length = table.getn(arg)
while true do
local arg_list = map(function(arr) return arr[i] end, arg)
if table.getn(arg_list) < arg_length then return new_array end
new_array[i] = func(unpack(arg_list))
i = i+1
end
end
These work as expected.
I then define zip and transpose as:
function zip(...)
return mapn(function(...) return {...} end,...)
end
function transpose(...)
return zip(unpack(...))
end
Now transpose({{1,2},{3,4},{5,6}}) produces {{1,3,5},{2,4,6}} as expected.
But transpose({{1,2},{3,4},{5}}) does not produce {{1,3,5},{2,4}}. It only produces one row.
How can I get it to produce the result I wish for?
I just decided to write an "inelegant" function instead. It seems there's no smooth way to use mapn and friends.
function transp(L)
local n=#L
local m,M=1e42,0
--Get the beginning and end of resultant transpose list.
for i=1,n do
for k,v in pairs(L[i]) do
if M<k then M=k end
if m>k then m=k end
end
end
local nt={}
for i=m,M do
local rt={}
for j=1,n do
rt[j]=L[j][i]
end
table.insert(nt,rt)
end
return nt
end
Please critique and improve this candidate solution.
I fixed a few things in your code and I think it works now as intended, I've added comments inline.
function map(func, array)
local new_array = {}
for i, v in ipairs(array) do
new_array[#new_array + 1] = func(v)
end
return new_array
end
function mapn(func, ...)
-- Variadic arguments bound to an array.
local arrays = {...}
local new_array = {}
-- Simple for-loop.
local i = 1
while true do
local arg_list = map(function(arr) return arr[i] end, arrays)
if #arg_list == 0 then
break
end
new_array[i] = func(unpack(arg_list))
i = i + 1
end
return new_array
end
-- Using 'mapn' instead of 'map' (probably how you intended).
function zip(...)
return mapn(function(...) return {...} end,...)
end
-- Same as before.
function transpose(...)
return zip(unpack(...))
end
Usage example:
for _, row in pairs(transpose({{1,2},{3,4},{5}})) do
for _, col in pairs(row) do io.write(col .. ' ') end
io.write('\n')
end
-- Output: 1 3 5
-- 2 4
The {5} in your example is being ignored because of this line:
if table.getn(arg_list) < arg_length then return new_array end
What you may want to do instead is break out of the loop only when arg_list is empty.
This will then give the result you want provided that the rows are monotonically increasing in length.
For the more general case, when later rows may be shorter than earlier ones
(e.g. {{1,2},{3,4,5},{6}}), you will need to keep track of the row lengths to allow for holes. This can be done by adding an optional argument (and extra return value) to map to indicate the maximum index i for which func(array[i]) was evaluated:
function map(func, array, len)
local new_array = {}
len = len or #array
for i=1,len do
new_array[i] = func(array[i])
end
return new_array, len
end
function mapn(func, ...)
local new_array = {}
local i=1
local arg_length = select('#', ...)
local args = {...}
while true do
local arg_list, num_results = map(function(arr) return arr[i] end, args, arg_length)
if not next(arg_list) then return new_array end
new_array[i] = func(unpack(arg_list, 1, num_results))
i = i+1
end
end
function zip(...)
return mapn(function(...) return {...} end,...)
end
function transpose(...)
return zip(unpack(...))
end