先附上代码：
//自定义结构体类型，进行大小比较
struct Games {
var winCount: Int
var loseCount: Int
}
let g1 = Games(winCount: 2, loseCount: 2)
let g2 = Games(winCount: 3, loseCount: 1)
extension Games: Comparable {} //此协议的实现方法写在外面
//协议方法实现的逻辑由编程者自己定义，要符合常规的逻辑
//<是方法名
func <(b1: Games, b2: Games) -> Bool {
let gScore1 = b1.winCount - b1.loseCount
let gScore2 = b2.winCount - b2.loseCount
return gScore1 < gScore2
}
g1 < g2跳转过去得到系统标准库中Comparable的协议如下：
public protocol Comparable : Equatable {
/// A [strict total order](http://en.wikipedia.org/wiki/Total_order#Strict_total_order)
/// over instances of `Self`.
@warn_unused_result
public func <(lhs: Self, rhs: Self) -> Bool
@warn_unused_result
public func <=(lhs: Self, rhs: Self) -> Bool
@warn_unused_result
public func >=(lhs: Self, rhs: Self) -> Bool
@warn_unused_result
public func >(lhs: Self, rhs: Self) -> Bool
}问题是：
1.swift中协议里面声明的方法不是都需要实现的吗，这里为什么不需要？
2.Comparable协议的方法为什么是在{ }外实现的？
伊谢尔伦2017-04-18 09:38:51
Equatable
Equatable协议：必须实现==方法，根据比较双方的数据类型来选择所对应的==方法。
struct Games {
var winCount: Int
var loseCount: Int
}
let g1 = Games(winCount: 2, loseCount: 2)
let g2 = Games(winCount: 3, loseCount: 1)
//g1 == g2 错误：自定义类型判断是否相等需要遵守协议Equatable，并实现相应方法
extension Games: Equatable {} //此协议只声明了一个方法，方法的实现可以在外面
//==为方法名，因为此协议方法是通过==来调用
func ==(b1: Games, b2: Games) -> Bool {
return b1.winCount == b2.winCount && b1.loseCount == b2.loseCount
}Comparable
Comparable协议：继承自Equatable必须实现Equatable中的==方法，还必须实现<方法。
extension Games: Comparable {
//注：对Games数据类型的==方法已经在上面实现，这里可以不用再写。
//协议的实现方法可以写在内部，类型方法在结构体中需要加static
static func <(b1: Games, b2: Games) -> Bool {
let gScore1 = b1.winCount - b1.loseCount
let gScore2 = b2.winCount - b2.loseCount
return gScore1 < gScore2
}
}public protocol Comparable : Equatable {
/// Returns a Boolean value indicating whether the value of the first
/// argument is less than that of the second argument.
///
/// This function is the only requirement of the `Comparable` protocol. The
/// remainder of the relational operator functions are implemented by the
/// standard library for any type that conforms to `Comparable`.
///
/// - Parameters:
/// - lhs: A value to compare.
/// - rhs: Another value to compare.
public static func <(lhs: Self, rhs: Self) -> Bool
/// Returns a Boolean value indicating whether the value of the first
/// argument is less than or equal to that of the second argument.
///
/// - Parameters:
/// - lhs: A value to compare.
/// - rhs: Another value to compare.
public static func <=(lhs: Self, rhs: Self) -> Bool
/// Returns a Boolean value indicating whether the value of the first
/// argument is greater than or equal to that of the second argument.
///
/// - Parameters:
/// - lhs: A value to compare.
/// - rhs: Another value to compare.
public static func >=(lhs: Self, rhs: Self) -> Bool
/// Returns a Boolean value indicating whether the value of the first
/// argument is greater than that of the second argument.
///
/// - Parameters:
/// - lhs: A value to compare.
/// - rhs: Another value to compare.
public static func >(lhs: Self, rhs: Self) -> Bool
}Havthgem 的回答: Swift 静态库对于剩余的对比计算是有默认实现的，基于你自定义的 == 和 <
PHP中文网2017-04-18 09:38:51
/// Instances of conforming types can be compared using relational
/// operators, which define a [strict total order](http://en.wikipedia.org/wiki/Total_order#Strict_total_order).
///
/// A type conforming to `Comparable` need only supply the `<` and
/// `==` operators; default implementations of `<=`, `>`, `>=`, and
/// `!=` are supplied by the standard library:
///
/// struct Singular : Comparable {}
/// func ==(x: Singular, y: Singular) -> Bool { return true }
/// func <(x: Singular, y: Singular) -> Bool { return false }
///
/// **Axioms**, in addition to those of `Equatable`:
///
/// - `x == y` implies `x <= y`, `x >= y`, `!(x < y)`, and `!(x > y)`
/// - `x < y` implies `x <= y` and `y > x`
/// - `x > y` implies `x >= y` and `y < x`
/// - `x <= y` implies `y >= x`
/// - `x >= y` implies `y <= x`以上是来自 Comparable 协议的注释，要是还看不懂的话，就回复吧。