为什么在 init 块中初始化变量接口属性的代码不会编译？

Question

interface A {
    var a: Int
}

class AJunior : A {
    override var a: Int

    init {
        a = 3
    }
}

它不会编译因为

Property must be initialized or be abstract

但它已初始化。我知道我可以写：

override var a: Int = 3

但为什么第一个示例无法编译？我的猜测是它是一个错误或有意限制以简化编译器实现，但我不确定。

Answer 1

I reported this as a bug，但事实证明此行为是设计使然，因为：

you could have code in the init block that could observe the property in its uninitialized state

Why won't code that initializes a variable interface property in init block compile?