How does parameter for functions work in lua?

Question

So I got this chunk of code that for some reason is giving me a null exception on LOVE

function enemies_controller:spawnEnemy(x, y, rad)
enemy = {}
enemy.x = x
enemy.y = y
enemy.rad = rad
enemy.speedMulti = 1
table.insert(enemies_controller.enemies, enemy)
end

And the function calling it like this:

enemies_controller.spawnEnemy(100, 100, 50)

The thing is that is giving me a null exception on the enemy.rad when i draw, cause enemy.x takes the second function parameter and enemy.y the third, and none takes the first one... So i am unsure of what is happening

Answer 1

It's because using : creates a "self" parameter. (This is a typing shortcut because lots of people make functions with self parameters. It doesn't do anything special.)

function enemies_controller:spawnEnemy(x, y, rad)

is the same as

function enemies_controller.spawnEnemy(self, x, y, rad)

or in other words:

enemies_controller.spawnEnemy = function(self, x, y, rad)

Notice the difference between . and :.

A similar thing when you call it:

enemies_controller:spawnEnemy(100, 100, 50)

is the same as:

enemies_controller.spawnEnemy(enemies_controller, 100, 100, 50)

and the first one is probably how you're meant to call the function - there's no other reason they'd define it with :.

If you call

enemies_controller.spawnEnemy(100, 100, 50)

then you pass 100 as self, 100 as x and 50 as y and nil as rad