I have the following code
let moveDirections = ["East": CGPoint(x: 1.0, y: 0.0),
"North": CGPoint(x: 0.0, y: 1.0),
"South": CGPoint(x: 0.0, y: -1.0),
"West": CGPoint(x: -1.0, y: 0.0),
]
let direction = "South"
let cdx = moveDirections[direction]?.x
Why does it insert the ? Surely the moveDirections variable contents is not optional.
That's the case with any dictionary:
aDictionary["some key"] always returns an optional.
If key has a value, you get it, otherwise you get nil.
I have worked round this using the following code
let moveDirections: [(Double,Double)] = [(1.0, 0.0), // East
(0.0, 1.0), // North
(1.0, 1.0), // NorthEast
(-1.0, 0.0), // NorthWest
(0.0, -1.0), // South
(1.0, -1.0), // SouthEast
(-1.0, -1.0), // SouthWest
(-1.0, 0.0) // West
]
var directions = ["East","North","NorthEast","NorthWest","South","SouthEast","SouthWest","West"]
let id = directions.firstIndex(of: direction)
let dt = moveDirections[id!]
let dx = dt.0
let dy = dt.1
What is direction here ? I suppose let direction = "South"
let id = directions.firstIndex(of: direction)
So you force unwrap.
but test with
let direction = "south"
app crashes here, as expected.
let dt = moveDirections[id!]
Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value
So, that did not solve it.