[英]swift - Comparing structs that conform to a protocol
I have the following structs that represent a point or a line: 我有以下表示点或线的结构:
public struct Point{
let x : Double
let y : Double
init (x : Double, y : Double)
{
self.x = x
self.y = y
}
}
extension Point : Equatable{}
public func ==(lhs: Point, rhs: Point) -> Bool
{
return lhs.x == rhs.x && lhs.y == rhs.y
}
And 和
public struct Line {
let points : [Point]
init(points : [Point])
{
self.points = points
}
}
extension Line : Equatable {}
public func ==(lhs: Line, rhs: Line) -> Bool
{
return lhs.points == rhs.points
}
I want to be able to have a Shape protocol or struct that I can use to have Points and Lines and then I can compare between them. 我希望能够有一个Shape协议或结构,可以用来包含Points and Lines,然后可以在它们之间进行比较。 I tried to that with conforming protocol Shape but Swift compiler gives me an error when I want to compare a point with a line even though they are Shapes.
我尝试使用一致的协议Shape来实现这一点,但是当我想将点与直线进行比较时,即使它们是Shapes,Swift编译器也会给我一个错误。
Do I have to move from struct to classes? 我必须从结构转到类吗?
I think I may have to use generics but don't know exactly how to solve this issue. 我想我可能必须使用泛型,但不确切地知道如何解决此问题。 Thanks in advance for any guidance.
在此先感谢您的指导。
Edit1: 编辑1:
My approach to Shape protocol was really just trying stuff but nothing worked. 我使用Shape协议的方法实际上只是尝试尝试,但没有任何效果。 I tried the following:
我尝试了以下方法:
protocol MapShape : Equatable
{
func == (lhs: MapShape, rhs: MapShape ) -> Bool
}
I also changed the code for the Equatable extension for lines given the suggestion 根据建议,我还更改了Equatable扩展的代码
This topic is covered in the WWDC 2015 session video Protocol-Oriented Programming in Swift , and here is my attempt to apply that to your situation: 该主题在WWDC 2015会话视频Swift中的面向协议的编程中有所介绍,这是我尝试将其应用于您的情况:
You define a protocol Shape
and a protocol extension method isEqualTo:
: 您定义一个协议
Shape
和一个协议扩展方法isEqualTo:
::
protocol Shape {
func isEqualTo(other: Shape) -> Bool
}
extension Shape where Self : Equatable {
func isEqualTo(other: Shape) -> Bool {
if let o = other as? Self { return self == o }
return false
}
}
isEqualTo:
checks if the other element is of the same type (and compares them with ==
in that case), and returns false
if they are of different type. isEqualTo:
检查其他元素是否具有相同的类型(在这种情况下,将它们与==
进行比较),如果它们具有不同的类型,则返回false
。
All types which are Equatable
automatically conform to Shape
, so that we can just set 所有
Equatable
类型Equatable
自动符合Shape
,因此我们可以设置
extension Point : Shape { }
extension Line : Shape { }
(Of course you can add other methods to Shape
which should be implemented by all shape types.) (当然,您可以向
Shape
添加其他方法,该方法应由所有Shape
类型实现。)
Now we can define ==
for shapes as 现在我们可以为形状定义
==
func ==(lhs: Shape, rhs: Shape) -> Bool {
return lhs.isEqualTo(rhs)
}
and voilà, points and lines can be compared: 和点,可以比较点和线:
let p1 = Point(x: 1, y: 2)
let p2 = Point(x: 1, y: 3)
let l1 = Line(points: [p1, p2])
let l2 = Line(points: [p1, p2])
print(p1 == p2) // false
print(p1 == l1) // false
print(l1 == l2) // true
Remark: You have ==
for the Shape
type now, but I haven't figured out yet to how make Shape
conform to Equatable
. 备注:现在
Shape
类型为==
,但是我还不知道如何使Shape
符合Equatable
。 Perhaps someone else can solve that part (if it is possible). 也许其他人可以解决这一部分(如果可能)。
Please allow me to shorten and correct your code a bit: 请允许我稍微缩短并更正您的代码:
struct Point : Equatable {
let x : Double
let y : Double
}
func ==(lhs: Point, rhs: Point) -> Bool {
return lhs.x == rhs.x && lhs.y == rhs.y
}
struct Line : Equatable {
let a : Point
let b : Point
}
func ==(lhs: Line, rhs: Line) -> Bool {
return lhs.a == rhs.a && lhs.b == rhs.b
}
I think I know now what you want: 我想我现在知道您想要什么:
protocol Shape : Equatable {
}
struct Polygon : Shape {
let points : [Point]
}
func ==(lhs: Polygon, rhs: Polygon) -> Bool {
return lhs.points == rhs.points
}
struct Circle : Shape {
let center : Point
let radius : Double
}
func ==(lhs: Circle, rhs: Circle) -> Bool {
return lhs.center == rhs.center && lhs.radius == rhs.radius
}
Note: You have to implement ==
for every shape on its own, because every shape type has different properties 注意:您必须为每个形状
==
实现==
,因为每种形状类型都有不同的属性
If you want every Shape to have a certain method, you can just add the requirement to the protocol: 如果您希望每个Shape都有特定的方法,则可以将要求添加到协议中:
protocol Shape : Equatable {
func move(dx: Double, dy: Double) -> Self
}
and make every Shape conform to it: 并使每个Shape都符合它:
struct Polygon : Shape {
let points : [Point]
func move(dx: Double, dy: Double) -> Polygon {
return Polygon(points: points.map { Point(x: $0.x + dx, y: $0.y + dy) })
}
}
struct Circle : Shape {
let center : Point
let radius : Double
func move(dx: Double, dy: Double) -> Circle {
return Circle(center: Point(x: center.x + dx, y: center.y + dy), radius: radius)
}
}
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