是否可以将某些属性(例如类型)排除在结构复制过程中

Question

i具有以下结构，其中包含类。

import Foundation
func generateRichText(body: String?) -> NSMutableAttributedString? {
    if body == nil {
        return nil
    }
    // TODO: Some complex logic to decorate body string will be added soon...
    let myAttrString = NSMutableAttributedString(string: body!)
    return myAttrString
}
struct Note {
    var body: String?
    // Technique described in https://stackoverflow.com/a/25073176/72437
    var bodyAsRichText: NSMutableAttributedString? {
        mutating get {
            if (cachedBodyAsRichText == nil) {
                cachedBodyAsRichText = generateRichText(body: body)
            }
            return cachedBodyAsRichText
        }
    }
    // TODO: This is a class. I don't want it to be copied over during struct copy.
    // If it is copied during struct copy, both struct will be sharing the same
    // class instance.
    private var cachedBodyAsRichText: NSMutableAttributedString?
}
var note = Note()
note.body = "hello"
print("note.bodyAsRichText = (Unmanaged.passUnretained(note.bodyAsRichText!).toOpaque())")
var note_copy = note
print("note_copy.bodyAsRichText = (Unmanaged.passUnretained(note_copy.bodyAsRichText!).toOpaque())")

对于上述代码，输出将为

note.bodyAsRichText = 0x000055c035cfce70
note_copy.bodyAsRichText = 0x000055c035cfce70

我所需的输出是不同的结构实例，应该拥有自己的类实例(cachedBodyAsRichText(

因此，有没有办法将cachedBodyAsRichText排除在结构复制期间的复制？

Answer 1

您的解决方案不完整。这是一个完整正确的解决方案。

struct Note {
    var body: String = "" {
        didSet {
            cachedBodyAsRichText = nil
        }
    }
    var bodyAsRichText: NSAttributedString {
        mutating get {
            if (cachedBodyAsRichText == nil) {
                cachedBodyAsRichText = generateRichText(body: body)
            }
            return cachedBodyAsRichText!.copy() as! NSAttributedString
        }
    }
    private var cachedBodyAsRichText: NSAttributedString? = nil
}

您需要每次修改身体时清除缓存。一旦这样做，该对象是否在结构之间共享。