问题
Why UIImagePickerController.InfoKey type is struct not a string ,what is the benefit to use struct as a dictionary key instead of string?
public struct InfoKey : Hashable, Equatable, RawRepresentable {
public init(rawValue: String)
}
}
extension UIImagePickerController.InfoKey {
public static let mediaType: UIImagePickerController.InfoKey
public static let originalImage: UIImagePickerController.InfoKey // a UIImage
public static let editedImage: UIImagePickerController.InfoKey // a UIImage
public static let cropRect: UIImagePickerController.InfoKey // an NSValue (CGRect)
回答1:
It's simple, the benefit is the ability to check key values during compilation. This way, you won't be able to pass a String directly and if you do, you have to manually wrap it into a InfoKey structure, making your intention clear.
Most of the times you should be using one of the predefined constants.
An enum would be a better solution but probably that would break some existing code (and cannot be really enforced in Objective-C).
If Apple engineers were creating a new API today, they wouldn't probably even use a dictionary but they would use a custom object to pass the values to the delegate method.
来源：https://stackoverflow.com/questions/56147956/why-swift-use-a-struct-as-dictionary-key-instead-of-a-string-here