ruby packing variables and monkey patching - ruby

Question

Okay so this is the code:
class Board
attr_reader :size
def initialize n
#grid = Array.new(n) {Array.new(n,:N)}
#size = n * n
end
def [] position
row, col = position
#grid[row][col]
end
def []= position, val
row, col = position
#grid[row][col] = val
end
def num_ships
#grid.flatten.count(:S)
end
def attack position
if self[position] == :S
self[position] = :H
puts "you sunk my battleship"
return true
else
self[position] = :X
return false
end
end
def place_random_ships
max_ships = #size * 0.25
while self.num_ships < max_ships
row = rand(0...#grid.length)
col = rand(0...#grid.length)
position = [row,col]
self[position] = :S
end
end
end
But,
def place_random_ships
max_ships = #size * 0.25
while self.num_ships < max_ships
row = rand(0...#grid.length)
col = rand(0...#grid.length)
position = [row,col]
self[position] = :S
end
end
this works, and does what it's suppose to, but when I avoid packing [row,col] and add it directly it does not work.
def place_random_ships
max_ships = #size * 0.25
while self.num_ships < max_ships
row = rand(0...#grid.length)
col = rand(0...#grid.length)
self[row,col] = :S
end
end
I'm still new to programming, so please try to explain the issue to where I can understand it, or tell me the problem, so I can google it to get a better understanding please.

Answer 1

The issue is that you defined []= to take 2 argument, and array and a value.
def []= position, val
row, col = position
#grid[row][col] = val
end
With your current implementation you would need to call it like this
foo[[row,col]] = :S
What you might want to to is define []= like this:
def []= row, col, val
#grid[row][col] = val
end
then when you want to pass the array position you can use the array spread operator. With this implementation both of these calls will work.
position = [1,2]
foo[1,2] = :S
foo[*position] = :S
if you do that you probably would want to define [] the same way.
def [] row,col
#grid[row][col]
end