swift - 这是什么意思 : "You do not have to provide an explicit implementation of a required initializer if you can satisfy the requirement"?

Question

我在关于初始化器的 Swift 文档中找到了这条注释:

You do not have to provide an explicit implementation of a required initializer if you can satisfy the requirement with an inherited initializer.

什么是“显式”实现？那么什么是“隐式”？

“用继承的初始化程序满足要求” 的确切含义是什么？

你能给我一个代码示例吗？我不必在其中提供所需初始化程序的显式实现？

Answer 1

这是一个带有内联解释的示例:

protocol JSONInitializable { // Use Encoders, but just for example
    init(fromJSON: String)
}

class Foo: JSONInitializable  {
    let x: Int

    // "required" is necessary because this init is required for the 
    // conformance to JSONInitializable
    required init(fromJSON json: String) {
        //...
        x = 123 //some value from the JSON
    }
}

class Baz: Foo {
    // `init(fromJSON json: String)` can be inherited,
    // so it's implicitly defined for Baz, as well as Foo.
}

class Bar: Foo {
    // The presence of this uninitialized constant `y` requires an
    // a value in the declaration, or an initializer that sets it
    let y: Int

    // Since we didn't specify a value for `y` in its declaration,
    // this initializer must be explicitly specified so as to initialize `y`.
    // Doing so blocks the inheritance of `init(fromJSON json: String)` from
    // the super class, and requires us to define it ourselves,
    // in order to preserve conformance to `JSONInitializable`
    required init(fromJSON json: String) {
        //...
        y = 0
        super.init(fromJSON: json)
    }
}