Objective-C float #define not accessible in Swift4 - objective-c

Question

I am migrating code from Objective-C to Swift 4.0. Here I have some float #define constants related to my deviceHeight in Specific Objective-C header class. While accessing this #define giving error "Use of unresolved identifier". When I use Objective-C string #define identifier it's easily accessible within Swift class.
Not accessible in Swift4
#define PHONE_IPHONE10 PHONE_UISCREEN_HEIGHT==812.0f
Accessible in Swift4
#define ERROR #"Some error occured. Please try later."
Help me with your comments or solution.

Answer 1

The reason this imports to Swift...
#define ERROR #"Some error occured. Please try later."
...is that it’s semantically equivalent to a constant declaration. That is, it permanently associates that string-literal value with the name ERROR. The Swift compiler recognizes that you’re using the C preprocessor to define a constant, and translates it to a Swift constant.
(Even though you could—and probably should—define C global constants without the preprocessor, Swift recognizes that there’s a long tradition of using #define instead, and imports it anyway.)
The reason this doesn’t import to Swift...
#define PHONE_IPHONE10 PHONE_UISCREEN_HEIGHT==812.0f
...is that this is a preprocessor macro. It doesn’t statically map a name to a value. Instead, it tells C that wherever it sees your name PHONE_IPHONE10, it should substitute the expression PHONE_UISCREEN_HEIGHT==812.0f. Presumably PHONE_UISCREEN_HEIGHT is itself a macro, so the whole thing expands to a chain of method calls and an equality comparison.
Swift itself doesn’t do preprocessor macros, or anything like such, so it doesn’t import them from C.
A close equivalent would be to redefine this logic using a computed property or function (and the idiomatic way to do that in Swift would be as a static member on a type, not a global symbol). Something like this:
extension UIDevice {
class var isMaybeiPhoneX: Bool {
return false // or some logic based on UIScreen.main.size
}
}
But be warned, the whole idea of conditionally changing your app’s UI or behavior based on a specific screen height check is fraught with peril. Tried Auto Layout?

Answer 2

To achieve similar functionality I created Constants.swift file with this structure:
struct Constants {
struct phoneHeights {
static let PHONE_UISCREEN_HEIGHT = 812.0
//some others consts
}
struct iPhoneX {
static let statusBarHeight: CGFloat = 44
//some others consts
}
}
Or simply:
struct Constants {
static let PHONE_UISCREEN_HEIGHT = 812.0
static let statusBarHeight: CGFloat = 44
}
And for type safety in Swift, you can read here.