Ruby For loop isn't running as expected - ruby

Question

I have this array of arrays:
WIN_COMBINATIONS = [
[0,1,2],
[3,4,5],
[6,7,8],
[0,3,6],
[0,4,8],
[6,4,2],
[1,4,7],
[2,5,8]
]
and I am defining this method:
def won?(board)
for x in WIN_COMBINATIONS
win_index_1 = x[0]
win_index_2 = x[1]
win_index_3 = x[2]
p1 = board[win_index_1]
p2 = board[win_index_2]
p3 = board[win_index_3]
if p1 == 'X' && p2 == 'X' && p3 == 'X'
return x
else
false
end
end
end
and when
board = [' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ']
The won? method returns every item in WIN_COMBINATIONS instead of false. I have no idea why and I would appreciate it if someone would please help.

Answer 1

In ruby each block, returns something even if you don't explicitly return a value, in your case the for block is returning the collection over you are iterating I think that your logic is correct but you need to make a small change, something like:
def won?(board)
for x in WIN_COMBINATIONS
win_index_1 = x[0]
win_index_2 = x[1]
win_index_3 = x[2]
p1 = board[win_index_1]
p2 = board[win_index_2]
p3 = board[win_index_3]
return x if p1 == "X" && p2 == "X" && p3 == "X"
end
false
end
The code above will return x if any of the sequences are valid, false in any other case (although you should follow the convention and return true or false if you are using the signature ?, other option is remove the ? and return nil instead of false). Hope this helps! 👍

Answer 2

Every block of code returns a value even if there is no explicit return keyword. for loop returns itself. With board = [' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '] you never hit the return x statement and you get WIN_COMBINATIONS back.
If you replace return false with return [], it will allow you to avoid 'expected a collection that can be converted to an array with #to_ary or #to_a, but got false'. But Ruby has a bunch of nice methods to work with arrays.
By convention, methods that end with ? should return a boolean value. Your method returns an array when the if statement is true.
In your case, I'd rename the method and use the find method to iterate through WIN_COMBINATIONS:
def find_win_combination(board)
# You can use decomposition as in the next example `do |wi_0, wi_1, wi_2|`
win_combination = WIN_COMBINATIONS.find do |combination|
win_index_0 = combination[0]
win_index_1 = combination[1]
win_index_2 = combination[2]
# If it's true the find method will return the win combination
board[win_index_0] == "X" && board[win_index_1] == "X" && board[win_index_2] == "X"
end
# return an empty array if win_combination is not found
win_combination || []
end
board = [' ', ' ', ' ', 'X', 'X', 'X', ' ', ' ', ' ']
> find_win_combination(board)
=> [3, 4, 5]
board = [' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ']
> find_win_combination(board)
=> []
If you need won? method to return a boolean method, just use any? method on WIN_COMBINATIONS. The result of any? will be returned as a result of won`?
def won?(board)
# Here is a decomposition of each item of `WIN_COMBINATIONS` into three variables
WIN_COMBINATIONS.any? do |wi_0, wi_1, wi_2|
board[wi_0] == "X" && board[wi_1] == "X" && board[wi_2] == "X"
end
end
board = [' ', ' ', ' ', 'X', 'X', 'X', ' ', ' ', ' ']
> won?(board)
=> true
board = [' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ']
> won?(board)
=> false