Within my updateBlob function, Xcode warned me that pos is unchanged and should be changed to a let constant, even though I can see that it's being changed, and running the program does indeed change the position values. This all seemed to happen when I updated the BlobPos class with a defer keyword to update the x/y coordinates when it is sent the radius value. Although I could avoid using defer, why does the compiler warn me of making pos a constant, and the program is still able to change what should presumably be a constant?
class BlobPos
{
var x:CGFloat = 0
var y:CGFloat = 0
public init(radius:CGFloat) {
defer {
x = radius + 5
y = radius + 5
}
}
}
class Blob
{
var radius: CGFloat
var pos: BlobPos
init
(
radius: CGFloat,
pos: BlobPos,
)
{
self.radius = radius
self.pos = pos
}
}
func makeBlob() -> Blob
{
let radius = 8
let pos = BlobPos(radius:radius)
return Blob(radius: radius, pos: pos)
}
func updateBlob(blob:Blob)
{
let radius = blob.radius
let pos = blob.pos // compiler warning wanting me to turn this into a let constant instead of var
pos.x += 6
pos.y += 2
blob.pos = pos // strangely, new position is set
}
That is because BlobPos is a class and changing a class's properties doesn't change its location in memory, which is how classes are passed around (by reference to their location in memory). If BlobPos were a structure, then you would have to declare it a variable because structures are passed around by their values (not references to their locations in memory).