Swift嵌套类属性

Question

swift没有嵌套类吗？

例如,我似乎无法从嵌套类访问主类的属性测试.

class master{
  var test = 2;

  class nested{
     init(){
       let example = test; //this doesn't work
     }
   }
 }

Answer 1

Swift的嵌套类与Java的嵌套类不同.好吧,它们就像是一种Java的嵌套类,但不是你想到的那种.

在Java中,内部类的实例自动具有对外部类的实例的引用(除非声明内部类static).如果您有外部类的实例,则只能创建内部类的实例.这就是为什么在Java中你会说出类似的东西this.new nested().

在Swift中,内部类的实例独立于外部类的任何实例.就好像Swift中的所有内部类都是使用Java声明的static.如果希望内部类的实例具有对外部类的实例的引用,则必须将其显式化:

class Master {
    var test = 2;

    class Nested{
        init(master: Master) {
            let example = master.test;
        }
    }

    func f() {
        // Nested is in scope in the body of Master, so this works:
        let n = Nested(master: self)
    }
}

var m = Master()
// Outside Master, you must qualify the name of the inner class:
var n = Master.Nested(master:m)

// This doesn't work because Nested isn't an instance property or function:
var n2 = m.Nested()

// This doesn't work because Nested isn't in scope here:
var n3 = Nested(master: m)