I was trying to access a member of 'self', see following:
function BasePlayer:blah()
--do blah
end
function BasePlayer:ctor(tape) --constructor.
self.tape = tape --'tape' is a lua table, and assigned to 'self.tape'.
dump(self.tape) --i can dump table 'self.tape',obviously it's not nil.
self.coreLogic = function(dt) --callback function called every frame.
echoInfo("%s",self) --prints self 'userdata: 0x11640d20'.
echoInfo("%s",self.tape) -- Here is my question: why self.tape is nil??
self:blah() --even function too??
end
end
So my question is, in my callback function 'coreLogic', why 'self.tape' is nil but self is
vaild?
And functions can't be called either.
I'm really confused:S
When you define a function using the :, the implicit parameter is created on its own. When you are defining the function coreLogic, you'd need to pass it as the first argument:
self.coreLogic = function( self, dt )
and that would be the same as:
function self:coreLogic(dt)
self in itself doesn't exist.
Basically,
function BasePlayer:blah()
is same as writing:
function BasePlayer.blah( BasePlayer )
Related
hope you having great day , i'm test some stuff with lua, and i got some error
i have this codes in Object.lua
local Object = {name = "Object"}
Object.__index = Object
function Object.new()
local t = setmetatable({}, Object)
return t
end
function Object:keys(table)
local keyset={}
local n=0
for k,v in pairs(table) do
n=n+1
keyset[n]=k
end
return keyset
end
return Object
and i call Object.keys in "Other" script like this
local Object = require("lua.app.common.utils.Object")
local t = {
[1] = a,
[2] = b,
[3]= c
}
Object.keys(t)
and this cause error with
Exception has occurred: bad argument #1 to 'for iterator' (table expected, got nil),
because the parameter 'table' is passed as nil ( i don't know why thuogh debug mode just says its a nil)
on the other hand, if i fix object.keys(table) to object:keys(table), everything works fine, why this error happening?
Declaring the method keys with a colon adds an implicit self parameter as the first argument which requires you to call the method in the same way, using the colon.
Calling the method with the period notation expects you to supply the self parameter but because you only pass in t this is interpreted as self and then nil is added for your table parameter.
Declaring the method with a colon you actually have this
function Object:keys(self, table)
but calling it with the period means you have done this
Object.keys(t, nil)
hence the "table expected, got nil" error
I'm learning game development with LÖVE2D and Lua and lately I've been using a state machine class. I haven't coded the class myself, but I've went through the code and I think I pretty much got it, besides this one problem.
The thing is, I'm trying to prompt the class for its current state, just so I can use it inside an if, but no matter what, I cannot get it right.
Here's the relevant code of the class:
StateMachine = Class{}
function StateMachine:init(states)
self.empty = {
render = function() end,
update = function() end,
enter = function() end,
exit = function() end
}
self.states = states or {} -- [name] -> [function that returns states]
self.current = self.empty
end
function StateMachine:change(stateName, enterParams)
assert(self.states[stateName]) -- state must exist!
self.current:exit()
self.current = self.states[stateName]()
self.current:enter(enterParams)
end
What I'm basically trying to do is:
function StateMachine:is(stateName)
if self.current == self.states[stateName] then
-- this never executes
return true
end
return false
end
I've tried changing self.states[stateName] to other things to test it out and also tried printing stuff to the console to see why the comparison is never true. It seems self.current returns a pointer to a table and thus never matches whatever is on the other side of the comparison operator.
Thanks for your help!
self.current is set to the return value of self.states[stateName] in StateMachine:change
function StateMachine:change(stateName, enterParams)
...
self.current = self.states[stateName]() -- note the () indicating the call
This means, unless the return value is self, self.current will not be equal to the function or object self.states[stateName] that it is compared to in StateMachine:is
function StateMachine:is(stateName)
if self.current == self.states[stateName] then -- here we are comparing the function to the return value
I would suggest expanding your state object to have a :getName function that would return the stateName or to store the name in your StateMachine under a key such as currentStateName.
I had the exact same question & I'd like to add--perhaps some of the comments explain this in language I just didn't understand :D--but in the getCurrentState function I created I had to do this:
function StateMachine:getCurrentState()
variable = self.currentStateName
return variable
where ofc variable is just some placeholder. but I had to grab the reference that self.currentStateName was pointing to, otherwise the comparison always failed.
I'm creating a dynamic table method reference and trying pass a single param to the method. The dynamic method reference does work and the table method is called just as expected, however the completely not nil param I'm passing to the method is nil inside the method. Can you point out my error in these 2 lines?...
Here is a small working example that demonstrates. On first line in the Consider:Move method, mons is nil
local Consider = {}
function Consider:Move( mons )
print( 'Mons ' .. mons.type .. ' considering Move...')
actionChosen.score = 0
return actionChosen
end
local mons = { type = 'Blue' }
local actionPref = 'Move'
local considerAction = Consider[actionPref]
print( 'MonsterAI:chooseAction mons: ', mons.type )
local actionTest = considerAction( mons )
Functions defined using the colon operator hides an additional first self argument. function Consider:Move(mons) is syntactic sugar for function Consider.Move(self, mons).
Calling the function like considerAction(mons) sets the hidden self argument instead of the desired one.
You might want to pass the Consider table as self:
considerAction(Consider, mons)
Or, alternatively, define the function using the dot operator if you don't need self:
function Consider.Move(mons)
print('Mons ' .. mons.type .. ' considering Move...')
end
I have this.
components=require("components")
entity={}
--test---
function entity.test(x,y)
self ={}
self.id="test"
--self.position=components.position(x,y)
return self
end
return entity
In main i have this.
entities=require("entity")
function love.load()
test1=entities.test(100,200)
print(test1.id)
end
the output is ok, but, when I add another component .
components=require("components")
entity={}
--test---
function entity.test(x,y)
self ={}
self.id="test"
self.position=components.position(x,y)
return self
end
return entity
and make another print
entities=require("entity")
function love.load()
test1=entities.test(100,200)
print(test1.id)
print(test1.position.y)
end
I got first a nill valur, and then an error because field position is nill. What happen? Thanks in advance.
my component.lua
component = {}
--position--
function component.position(x,y)
self={}
self.x=x
self.y=y
return self
end
return component
You can fix the problem by declaring your variables local, e.g. local self = {}.
When you call entity.test, that function assigns a new table to the global self. It then calls components.position which assigns a whole new table to self, which never gets the position field.
i have code in my lua file and i edit that to look like this
function getUserinfo(user_id)
function call_back_user_info(status , result)
t = {["first_name"]= result.first_name_, ['have_access']= result.have_access_, ["last_name"]=result.last_name_,["user_name"]=result.username_}
return t
end
getUser(user_id,call_back_user_info)
end
i need to return t table value when i call getUserinfo function.but it is get me a nil value !
note :getUser function puts data in to call_back_user_info
how i can resolve this problem? thank
You can't do a "long return" which returns from an outer function from inside of an inner function.
But what you can do is create a local variable which is closed over, like this:
function getUserinfo(user_id)
local t
function call_back_user_info(status , result)
t = {["first_name"]= result.first_name_,
['have_access']= result.have_access_,
["last_name"]=result.last_name_,
["user_name"]=result.username_}
end
getUser(user_id,call_back_user_info)
return t
end