How to pass a function by refference

[Rob.m]

Hi,

I have this code -

Code: Select all

function love.load()
  button = {text = "Hello World", x = 0, y = 0, r = 0, sx = 1, sy = 1, ox = 0, oy = 0, kx = 0, ky = 0}
  button.click = mouseclick(button)
  button.x = 0
end

function love.draw()
  local ob = button
  love.graphics.print(ob.text, ob.x, ob.y, ob.r, ob.sx, ob.sy, ob.ox, ob.oy, ob.kx, ob.ky)
end

function love.mousepressed()
  dummy = button.click
end

function mouseclick(lob)
  lob.x = 100
  lob.text = "Clicked"
end

What I get here is the text ;clicked; at the x position 0 before I click. then when I click nothing happens. I expected the x pos to be set to 100

It is evaluating mouseclick(button) with the statement button.click = mouseclick(button)

and dummy = button.click doesn't seem to be doing anything.

From wat I have read, simple single dimentional variables are passed as a value and anything else (data structures) are passed by refference.

It seems that a function that is refferenced at the time of entry to a data structure is evaluated at that time and that time only.

So how do I pass a function by refference alone?

[pakoskyfrog]

Hellö !

Functions are in lua, just like any variables. However if you use the () syntax you will make a function call.
So, either you pass the function as it is : button.click = mouseclick
or you make a function that will return a function :

Code: Select all

local factory = function (btn)
    return function (x, y, b)
        -- your code here
    end
end

button.click = factory(button)

dummy = button.click

Actually this assign button.click into the global variable 'dummy' (and that's ugly:P)

And i think you should use some kind of OOP with the ':' and the self. For instance : (and if i understood you well, this should do what you intended to)

Code: Select all

function love.load()
  button = {text = "Hello World", x = 0, y = 0, r = 0, sx = 1, sy = 1, ox = 0, oy = 0, kx = 0, ky = 0}
  button.click = mouseclick
  -- button.x = 0 -- not needed since you already have x=0 in button = { ... }
end

function love.draw()
  local ob = button
  love.graphics.print(ob.text, ob.x, ob.y, ob.r, ob.sx, ob.sy, ob.ox, ob.oy, ob.kx, ob.ky)
end

function love.mousepressed()
  button:click()
  -- equivalent to button.click(button)
  --  or mouseclick(button)
end

function mouseclick(self)
  self.x = 100
  self.text = "Clicked"
end

This is not tested but should work anyway

[Kadoba]

What I get here is the text ;clicked; at the x position 0 before I click. then when I click nothing happens. I expected the x pos to be set to 100

That is because as soon as the button.x is set to 100 when calling mouseclick() it's immediately set it to 0 afterwards.

It is evaluating mouseclick(button) with the statement button.click = mouseclick(button)

and dummy = button.click doesn't seem to be doing anything.

The function is being called but it doesn't return anything so dummy is set to nil.

From wat I have read, simple single dimentional variables are passed as a value and anything else (data structures) are passed by refference.

It seems that a function that is refferenced at the time of entry to a data structure is evaluated at that time and that time only.

So how do I pass a function by refference alone?

In Lua functions are first-class citizens so the concepts of pass-by-reference and pass-by-value don't really apply. It's a little bit of both.

I'm not completely sure what your code is suppose to do so I'm going to assume you just mean to record and print a message at the mouse click location. If that's the case this should work:

Code: Select all

local button = {text = "Hello World", x = 0, y = 0, r = 0, sx = 1, sy = 1, ox = 0, oy = 0, kx = 0, ky = 0}

function love.draw()
  local ob = button
  love.graphics.print(ob.text, ob.x, ob.y, ob.r, ob.sx, ob.sy, ob.ox, ob.oy, ob.kx, ob.ky)
end

function love.mousepressed(x,y,mb)
    button.x = x
    button.y = y
    button.text = "Clicked"
end

I hope that helps.