Passing key in function

[knuxyl]

So I have a very complex/optimized idea of dealing with stacks for drawing and inputs but I've hit a barrier.

I have declared a function like this

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function ui:input()
    do stuff
end

And then I have that stored into a table

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function stack:push()
    table.insert(stack.input, function() ui:input() end)
end

Now the problem I am running into is this code below

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function love.keypressed(key)
	stack.input[#stack.input](key)
end

It is returning key as nil when the function is executed. I tried passing self as the first argument but that did not work either.

My goal is to have a dynamic way of calling different inputs and draws without filling my code with if's. I've got the draw functions down perfect, I'm just stuck with this. I've read there might be a problem with dot and colon notation for the functions but passing self didn't work.

Any ideas or a better way of handling stacks? Thanks!

[pgimeno]

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function stack:push()
    table.insert(stack.input, function() ui:input() end)
end

Now the problem I am running into is this code below

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function love.keypressed(key)
	stack.input[#stack.input](key)
end

If it doesn't specify any arguments, every argument you pass will be ignored. Maybe you want this instead?

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function stack:push()
    table.insert(stack.input, function(...) ui:input(...) end)
end

I'm not sure how you intend to distinguish types of input, though. Perhaps you could pass the name of the triggering event, like this:

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function love.keypressed(...)
	stack.input[#stack.input]("keypressed", ...)
end

[knuxyl]

Adding the ... in function() and ui:input() seems to have fixed the issue. What exactly does this do? Is this just a placeholder letting lua know it should have an argument or do the 3 dots actually mean something? Thanks!

[pgimeno]

Adding the ... in function() and ui:input() seems to have fixed the issue. What exactly does this do? Is this just a placeholder letting lua know it should have an argument or do the 3 dots actually mean something? Thanks!

When used in a function declaration, it indicates that it accepts a variable number of arguments. It can only be additionally used within functions that have ... in the function declaration, and in that case, it means a tuple of all of the arguments passed. For example (using this distinction between arguments and parameters):

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-- function with two arguments
function x(a, b)
  print(a, b)
end

-- Function declaration with no parameters
function y()
  -- we can't use "..." here because it's not in the declaration
  x()  -- call function x with no arguments
  -- when a function is called with fewer arguments than parameters,
  -- the missing parameters are set to nil, so this is equivalent
  -- to: x(nil, nil)
end

-- Function declaration with variable number of arguments
function z(...)
  -- we can use "..." here because we're in a function declared with "..."
  x(...)  -- passes all arguments we were passed as arguments of function x
end

-- "..." is illegal at this point because we're not inside a function declaration

x(1, 2)  -- prints 1, 2
y(1, 2)  -- we can do this, but since the declaration says that y() has no parameters,
         -- the 1 and 2 are lost, and this prints nil, nil
z(1, 2)  -- prints 1, 2

[knuxyl]

Adding the ... in function() and ui:input() seems to have fixed the issue. What exactly does this do? Is this just a placeholder letting lua know it should have an argument or do the 3 dots actually mean something? Thanks!

When used in a function declaration, it indicates that it accepts a variable number of arguments. It can only be additionally used within functions that have ... in the function declaration, and in that case, it means a tuple of all of the arguments passed. For example (using this distinction between arguments and parameters):

Code: Select all

-- function with two arguments
function x(a, b)
  print(a, b)
end

-- Function declaration with no parameters
function y()
  -- we can't use "..." here because it's not in the declaration
  x()  -- call function x with no arguments
  -- when a function is called with fewer arguments than parameters,
  -- the missing parameters are set to nil, so this is equivalent
  -- to: x(nil, nil)
end

-- Function declaration with variable number of arguments
function z(...)
  -- we can use "..." here because we're in a function declared with "..."
  x(...)  -- passes all arguments we were passed as arguments of function x
end

-- "..." is illegal at this point because we're not inside a function declaration

x(1, 2)  -- prints 1, 2
y(1, 2)  -- we can do this, but since the declaration says that y() has no parameters,
         -- the 1 and 2 are lost, and this prints nil, nil
z(1, 2)  -- prints 1, 2

Perfect, thanks so much for your help! One more question, if ... is more than one variable, then is it stored as a table? like to reference the second variable in the passed arguments, would it be like this

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function something(...)
   x = ...
   print(x[2])
end

[pgimeno]

Perfect, thanks so much for your help! One more question, if ... is more than one variable, then is it stored as a table? like to reference the second variable in the passed arguments, would it be like this

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function something(...)
   x = ...
   print(x[2])
end

No, it's a tuple, not a table. However, you can pass a tuple to a table constructor and then you can do what you want. Tuples are just multiple values, and they are handled specially.

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function something(...)
  local a, b = ...  -- sets a to the first element and b to the second, ignores the rest
  local x = {...}   -- constructs a table with all arguments
  print(x[2])       -- prints the second argument (taking it from the table)
  print(b)          -- prints the same
  local c = select(2, ...)
  print(c)          -- prints the same
end

select() is a system function that takes an index (or the string "#") and returns all arguments starting in that position (or the number of arguments):

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  print(select(2, "a", "b", "c"))    -- prints:  b    c
  print(select(3, "a", "b", "c"))    -- prints:  c
  print(select("#", "a", "b", "c"))  -- prints:  3

When you pass it '...', each element in the tuple is passed as an additional argument, and select() returns the argument at the index you want.

[knuxyl]

Ok I'll look into that later, now my problem is my functions that are stored in the stack are not properly returning values.

lets say i have this

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function ui:menu(var)
    pseudo create menu var
    return false
end

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function stack:push(fun)
    table.insert(stack.fun, fun)
end

love.load

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stack:push(function() ui:menu(main) end)

and in love.update

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for i in ipairs(stack.fun) do
    check = stack.fun[i]()
    print(check)
end

love.draw is only drawing the canvas

From my understanding, since the menu creation function is being stored in the stack and called in love.update, check should be storing the returned variable, but it's not, it's returning nil. I need it to return a boolean to check whether it should be rendered again or not. I'm using a canvas to limit the amount of code being processed every tick and this would stop unnecessary code from running.

I've never really worked with return from functions before.

[MrFariator]

You need to do this one little change:

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stack:push(function() return ui:menu(main) end) -- note the 'return' here

However, keep in mind that this will create a function every single time this particular line of code is run, which may or may not be ideal depending on how often this is run, or how you manage the 'stack'.

Additionally, if ui:menu() were to return multiple values, then in your loop you'd have to assign those individually:

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for i in ipairs(stack.fun) do
    check1,check2,check3 = stack.fun[i]()
    print(check1,check2,check3)
end

But if you only want to print the return values, wrapping the function call in a print works:

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local function func2 ()
  return 1,2,3
end
local function func1 ()
  return func2()
end
local val = func1()
print(val)     -- prints 1
print(func1()) -- prints 1 2 3

[knuxyl]

Pefect!!! Yeah I have most functions turn off right after they are ran, inside the for loop i do a check on stack.exe to see if it's true or false, if true ill run the code. my push functions only are ran when needed, everything else is handed by the returned boolean. Thanks so much!!!