ios - swift 这些协议(protocol)有什么区别

Question

我见过以两种方式声明协议(protocol)，但我不明白其中的区别。

示例 1:

protocol AddItemViewControllerDelegate {
    func controller(controller: AddItemViewController, didAddItem: String)
}

例子2:

protocol AddItemViewControllerDelegate: class {
    func controller(controller: AddItemViewController, didAddItem: String)
}

那么有什么区别呢？

Answer 1

来自文档:

You can limit protocol adoption to class types (and not structures or enumerations) by adding the class keyword to a protocol’s inheritance list. The class keyword must always appear first in a protocol’s inheritance list, before any inherited protocols:

protocol SomeClassOnlyProtocol: class, SomeInheritedProtocol {
// class-only protocol definition goes here }

注意:

Use a class-only protocol when the behavior defined by that protocol’s requirements assumes or requires that a conforming type has reference semantics rather than value semantics.