joshuahall / elm-2d-array Goto Github PK

Hi!
I recently had a bug when searching for neighbours in an Array2D.
It looks like when calling Array2D.get with a negative column will return values from the previous row, if any, starting from the end.

array = Array2D.fromRows <|
    Array.fromList
        [ Array.fromList [ 1, 2 ]
        , Array.fromList [ 3, 4 ]
        ]

result = Maybe.map (Array.get 1 -1) array -- returns (Just 2) instead of Nothing

Please see the following Ellie: https://ellie-app.com/gbCSDCn2r9ka1

Is it intended behaviour?

[EDIT]

If is not intended behaviour, I guess I could add a check against row/column begin greater than numRows/numColumns here:

get : Int -> Int -> Array2D a -> Maybe a
get row column (InternalArray2D array) =
    if row >= array.numRows || column >= array.numColumns then
        Nothing

    else
        Array.get
            (indexFromRowAndColumn (InternalArray2D array) row column)
            array.array

In the first example indices are correct in the provided function, but in the second example, you can see that the indices are wrong.
I think the problem occurs when rows are greater than cols.

Array2D.initialize 4 4 (\row col -> (String.fromInt row ++ ":" ++ String.fromInt col))
["0:0","0:1","0:2","0:3"
,"1:0","1:1","1:2","1:3"
,"2:0","2:1","2:2","2:3"
,"3:0","3:1","3:2","3:3"
]

Array2D.initialize 4 2 (\row col -> (String.fromInt row ++ ":" ++ String.fromInt col))
["0:0","0:1"
,"0:0","0:1"
,"1:0","1:1"
,"1:0","1:1
]