Merge pull request scala#2821 from benluo/overviews/scala3-book/ca-extension-method

add code tabs in English and Chinese ca-extension-methods.md

Author: sjrd

_overviews/scala3-book/ca-extension-methods.md

@@ -17,33 +17,56 @@ In Scala 2, a similar result could be achieved with [implicit classes]({% link _
 Extension methods let you add methods to a type after the type is defined, i.e., they let you add new methods to closed classes.
 For example, imagine that someone else has created a `Circle` class:
 
+{% tabs ext1 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 case class Circle(x: Double, y: Double, radius: Double)
 ```
+{% endtab %}
+{% endtabs %}
 
 Now imagine that you need a `circumference` method, but you can’t modify their source code.
 Before the concept of term inference was introduced into programming languages, the only thing you could do was write a method in a separate class or object like this:
 
+{% tabs ext2 class=tabs-scala-version %}
+{% tab 'Scala 2' %}
+```scala
+object CircleHelpers {
+  def circumference(c: Circle): Double = c.radius * math.Pi * 2
+}
+```
+{% endtab %}
+{% tab 'Scala 3' %}
 ```scala
 object CircleHelpers:
   def circumference(c: Circle): Double = c.radius * math.Pi * 2
 ```
+{% endtab %}
+{% endtabs %}
 
 Then you’d use that method like this:
 
+{% tabs ext3 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 val aCircle = Circle(2, 3, 5)
 
 // without extension methods
 CircleHelpers.circumference(aCircle)
 ```
+{% endtab %}
+{% endtabs %}
 
 But with extension methods you can create a `circumference` method to work on `Circle` instances:
 
+{% tabs ext4 %}
+{% tab 'Scala 3 Only' %}
 ```scala
 extension (c: Circle)
   def circumference: Double = c.radius * math.Pi * 2
 ```
+{% endtab %}
+{% endtabs %}
 
 In this code:
 
@@ -52,19 +75,27 @@ In this code:
 
 Then in your code you use `circumference` just as though it was originally defined in the `Circle` class:
 
+{% tabs ext5 %}
+{% tab 'Scala 3 Only' %}
 ```scala
 aCircle.circumference
 ```
+{% endtab %}
+{% endtabs %}
 
 ### Import extension method
 
 Imagine, that `circumference` is defined in package `lib`, you can import it by
 
+{% tabs ext6 %}
+{% tab 'Scala 3 Only' %}
 ```scala
 import lib.circumference
 
 aCircle.circumference
 ```
+{% endtab %}
+{% endtabs %}
 
 The compiler also supports you if the import is missing by showing a detailed compilation error message such as the following:
 
@@ -81,11 +112,15 @@ The following import might fix the problem:
 The `extension` keyword declares that you’re about to define one or more extension methods on the type that’s put in parentheses.
 To define multiple extension methods on a type, use this syntax:
 
+{% tabs ext7 %}
+{% tab 'Scala 3 Only' %}
 ```scala
 extension (c: Circle)
   def circumference: Double = c.radius * math.Pi * 2
   def diameter: Double = c.radius * 2
   def area: Double = math.Pi * c.radius * c.radius
 ```
+{% endtab %}
+{% endtabs %}
 
 

_zh-cn/overviews/scala3-book/ca-extension-methods.md

@@ -13,37 +13,63 @@ layout: multipage-overview
 permalink: "/zh-cn/scala3/book/:title.html"
 ---
 
+在 Scala 2 中，用 [implicit classes]({% link _overviews/core/implicit-classes.md %}) 可以得到类似的结果。
+
+---
 
 扩展方法允许您在定义类型后向类型添加方法，即它们允许您向封闭类添加新方法。
 例如，假设其他人创建了一个 `Circle` 类：
 
+{% tabs ext1 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 case class Circle(x: Double, y: Double, radius: Double)
 ```
+{% endtab %}
+{% endtabs %}
 
 现在想象一下，你需要一个 `circumference` 方法，但是你不能修改它们的源代码。
 在将术语推理的概念引入编程语言之前，您唯一能做的就是在单独的类或对象中编写一个方法，如下所示：
 
+{% tabs ext2 class=tabs-scala-version %}
+{% tab 'Scala 2' %}
+```scala
+object CircleHelpers {
+  def circumference(c: Circle): Double = c.radius * math.Pi * 2
+}
+```
+{% endtab %}
+{% tab 'Scala 3' %}
 ```scala
 object CircleHelpers:
   def circumference(c: Circle): Double = c.radius * math.Pi * 2
 ```
+{% endtab %}
+{% endtabs %}
 
 你可以像这样用该方法：
 
+{% tabs ext3 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 val aCircle = Circle(2, 3, 5)
 
 // without extension methods
 CircleHelpers.circumference(aCircle)
 ```
+{% endtab %}
+{% endtabs %}
 
 但是使用扩展方法，您可以创建一个 `circumference` 方法来处理 `Circle` 实例：
 
+{% tabs ext4 %}
+{% tab 'Scala 3 Only' %}
 ```scala
 extension (c: Circle)
   def circumference: Double = c.radius * math.Pi * 2
 ```
+{% endtab %}
+{% endtabs %}
 
 在这段代码中：
 
@@ -52,19 +78,27 @@ extension (c: Circle)
 
 然后在您的代码中使用 `circumference`，就像它最初是在 `Circle` 类中定义的一样：
 
+{% tabs ext5 %}
+{% tab 'Scala 3 Only' %}
 ```scala
 aCircle.circumference
 ```
+{% endtab %}
+{% endtabs %}
 
 ### 导入扩展方法
 
 想象一下，`circumference` 定义在`lib` 包中，你可以通过以下方式导入它
 
+{% tabs ext6 %}
+{% tab 'Scala 3 Only' %}
 ```scala
 import lib.circumference
 
 aCircle.circumference
 ```
+{% endtab %}
+{% endtabs %}
 
 如果缺少导入，编译器还会通过显示详细的编译错误消息来支持您，如下所示：
 
@@ -81,9 +115,13 @@ The following import might fix the problem:
 `extension` 关键字声明您将要在括号中的类型上定义一个或多个扩展方法。
 要在一个类型上定义多个扩展方法，请使用以下语法：
 
+{% tabs ext7 %}
+{% tab 'Scala 3 Only' %}
 ```scala
 extension (c: Circle)
   def circumference: Double = c.radius * math.Pi * 2
   def diameter: Double = c.radius * 2
   def area: Double = math.Pi * c.radius * c.radius
 ```
+{% endtab %}
+{% endtabs %}