public protocol Equatable {
/// Returns a Boolean value indicating whether two values are equal.
///
/// Equality is the inverse of inequality. For any values `a` and `b`,
/// `a == b` implies that `a != b` is `false`.
///
/// - Parameters:
/// - lhs: A value to compare.
/// - rhs: Another value to compare.
static func == (lhs: Self, rhs: Self) -> Bool
}
协议仅有一个 static 的方法 ==
用来判断两个 数据 是否相等。
类似于OC的 isEqualTo: 方法。
举例：
struct Animation {
var name: String
var age: Int
}
extension Animation: Equatable {
static func ==(lhs: Self, rhs: Self) -> Bool {
return lhs.name == rhs.name
}
}
let dogA = Animation(name: "dog", age: 1)
let dogB = Animation(name: "dog", age: 2)
print(dogA == dogB)
输出：
true
