Merge pull request #2659 from alvinj/merge-type-class-lessons

bishabosha · web-flow · commit dd4da874c35a · 2022-12-16T09:56:00.000+01:00
undefined
diff --git a/_overviews/scala3-book/ca-context-bounds.md b/_overviews/scala3-book/ca-context-bounds.md
@@ -4,7 +4,7 @@ type: section
 description: This page demonstrates Context Bounds in Scala 3.
 languages: [zh-cn]
 num: 61
-previous-page: types-type-classes
+previous-page: ca-given-using-clauses
 next-page: ca-given-imports
 ---
 
diff --git a/_overviews/scala3-book/ca-contextual-abstractions-intro.md b/_overviews/scala3-book/ca-contextual-abstractions-intro.md
@@ -5,7 +5,7 @@ description: This chapter provides an introduction to the Scala 3 concept of Con
 languages: [zh-cn]
 num: 58
 previous-page: types-others
-next-page: ca-given-using-clauses
+next-page: ca-extension-methods
 ---
 
 
@@ -37,6 +37,10 @@ While these concepts were gradually “discovered” in Scala 2, they’re now w
 The design of Scala 3 focuses on **intent** rather than **mechanism**.
 Instead of offering one very powerful feature of implicits, Scala 3 offers several use-case oriented features:
 
+- **Retroactively extending classes**.
+  In Scala 2, extension methods had to be encoded using implicit conversions or implicit classes.
+  In contrast, in Scala 3 [extension methods][extension-methods] are now directly built into the language, leading to better error messages and improved type inference.
+
 - **Abstracting over contextual information**.
   [Using clauses][givens] allow programmers to abstract over information that is available in the calling context and should be passed implicitly.
   As an improvement over Scala 2 implicits, using clauses can be specified by type, freeing function signatures from term variable names that are never explicitly referred to.
@@ -45,10 +49,6 @@ Instead of offering one very powerful feature of implicits, Scala 3 offers sever
   [Given instances][type-classes] allow programmers to define the _canonical value_ of a certain type.
   This makes programming with type-classes more straightforward without leaking implementation details.
 
-- **Retroactively extending classes**.
-  In Scala 2, extension methods had to be encoded using implicit conversions or implicit classes.
-  In contrast, in Scala 3 [extension methods][extension-methods] are now directly built into the language, leading to better error messages and improved type inference.
-
 - **Viewing one type as another**.
   Implicit conversion have been [redesigned][implicit-conversions] from the ground up as instances of a type-class `Conversion`.
 
diff --git a/_overviews/scala3-book/ca-extension-methods.md b/_overviews/scala3-book/ca-extension-methods.md
@@ -3,9 +3,9 @@ title: Extension Methods
 type: section
 description: This page demonstrates how Extension Methods work in Scala 3.
 languages: [zh-cn]
-num: 63
-previous-page: ca-given-imports
-next-page: ca-type-classes
+num: 59
+previous-page: ca-contextual-abstractions-intro
+next-page: ca-given-using-clauses
 ---
 
 
diff --git a/_overviews/scala3-book/ca-given-imports.md b/_overviews/scala3-book/ca-given-imports.md
@@ -5,7 +5,7 @@ description: This page demonstrates how 'given' import statements work in Scala
 languages: [zh-cn]
 num: 62
 previous-page: ca-context-bounds
-next-page: ca-extension-methods
+next-page: ca-type-classes
 ---
 
 
diff --git a/_overviews/scala3-book/ca-given-using-clauses.md b/_overviews/scala3-book/ca-given-using-clauses.md
@@ -3,9 +3,9 @@ title: Given Instances and Using Clauses
 type: section
 description: This page demonstrates how to use 'given' instances and 'using' clauses in Scala 3.
 languages: [zh-cn]
-num: 59
-previous-page: ca-contextual-abstractions-intro
-next-page: types-type-classes
+num: 60
+previous-page: ca-extension-methods
+next-page: ca-context-bounds
 ---
 
 
diff --git a/_overviews/scala3-book/ca-implicit-conversions.md b/_overviews/scala3-book/ca-implicit-conversions.md
@@ -3,7 +3,7 @@ title: Implicit Conversions
 type: section
 description: This page demonstrates how to implement Implicit Conversions in Scala 3.
 languages: [zh-cn]
-num: 66
+num: 65
 previous-page: ca-multiversal-equality
 next-page: ca-summary
 ---
diff --git a/_overviews/scala3-book/ca-multiversal-equality.md b/_overviews/scala3-book/ca-multiversal-equality.md
@@ -3,7 +3,7 @@ title: Multiversal Equality
 type: section
 description: This page demonstrates how to implement Multiversal Equality in Scala 3.
 languages: [zh-cn]
-num: 65
+num: 64
 previous-page: ca-type-classes
 next-page: ca-implicit-conversions
 ---
diff --git a/_overviews/scala3-book/ca-summary.md b/_overviews/scala3-book/ca-summary.md
@@ -3,7 +3,7 @@ title: Summary
 type: section
 description: This page provides a summary of the Contextual Abstractions lessons.
 languages: [zh-cn]
-num: 67
+num: 66
 previous-page: ca-implicit-conversions
 next-page: concurrency
 ---
diff --git a/_overviews/scala3-book/ca-type-classes.md b/_overviews/scala3-book/ca-type-classes.md
@@ -1,16 +1,21 @@
 ---
-title: Implementing Type Classes
+title: Type Classes
 type: section
 description: This page demonstrates how to create and use type classes in Scala 3.
 languages: [zh-cn]
-num: 64
-previous-page: ca-extension-methods
+num: 63
+previous-page: ca-given-imports
 next-page: ca-multiversal-equality
 ---
 
 
 A _type class_ is an abstract, parameterized type that lets you add new behavior to any closed data type without using sub-typing.
-This is useful in multiple use-cases, for example:
+If you are coming from Java, you can think of type classes as something like [`java.util.Comparator[T]`][comparator].
+
+> The paper [“Type Classes as Objects and Implicits”][typeclasses-paper] (2010) by Oliveira et al. discusses the basic ideas behind type classes in Scala.
+> Even though the paper uses an older version of Scala, the ideas still hold to the current day.
+
+A type class is useful in multiple use-cases, for example:
 
 - Expressing how a type you don’t own---from the standard library or a third-party library---conforms to such behavior
 - Expressing such a behavior for multiple types without involving sub-typing relationships between those types
@@ -108,4 +113,7 @@ trait HasLegs[A]:
 For a real-world example of how type classes are used in Scala 3, see the `CanEqual` discussion in the [Multiversal Equality section][multiversal].
 
 
+[typeclasses-paper]: https://infoscience.epfl.ch/record/150280/files/TypeClasses.pdf
+[typeclasses-chapter]: {% link _overviews/scala3-book/ca-type-classes.md %}
+[comparator]: https://docs.oracle.com/javase/8/docs/api/java/util/Comparator.html
 [multiversal]: {% link _overviews/scala3-book/ca-multiversal-equality.md %}
diff --git a/_overviews/scala3-book/concurrency.md b/_overviews/scala3-book/concurrency.md
@@ -3,7 +3,7 @@ title: Concurrency
 type: chapter
 description: This page discusses how Scala concurrency works, with an emphasis on Scala Futures.
 languages: [zh-cn]
-num: 68
+num: 67
 previous-page: ca-summary
 next-page: scala-tools
 ---
diff --git a/_overviews/scala3-book/interacting-with-java.md b/_overviews/scala3-book/interacting-with-java.md
@@ -3,7 +3,7 @@ title: Interacting with Java
 type: chapter
 description: This page demonstrates how Scala code can interact with Java, and how Java code can interact with Scala code.
 languages: [zh-cn]
-num: 72
+num: 71
 previous-page: tools-worksheets
 next-page: scala-for-java-devs
 ---
diff --git a/_overviews/scala3-book/scala-for-java-devs.md b/_overviews/scala3-book/scala-for-java-devs.md
@@ -3,7 +3,7 @@ title: Scala for Java Developers
 type: chapter
 description: This page is for Java developers who are interested in learning about Scala 3.
 languages: [zh-cn]
-num: 73
+num: 72
 previous-page: interacting-with-java
 next-page: scala-for-javascript-devs
 ---
diff --git a/_overviews/scala3-book/scala-for-javascript-devs.md b/_overviews/scala3-book/scala-for-javascript-devs.md
@@ -3,7 +3,7 @@ title: Scala for JavaScript Developers
 type: chapter
 description: This chapter provides an introduction to Scala 3 for JavaScript developers
 languages: [zh-cn]
-num: 74
+num: 73
 previous-page: scala-for-java-devs
 next-page: scala-for-python-devs
 ---
diff --git a/_overviews/scala3-book/scala-for-python-devs.md b/_overviews/scala3-book/scala-for-python-devs.md
@@ -3,7 +3,7 @@ title: Scala for Python Developers
 type: chapter
 description: This page is for Python developers who are interested in learning about Scala 3.
 languages: [zh-cn]
-num: 75
+num: 74
 previous-page: scala-for-javascript-devs
 next-page: where-next
 ---
@@ -1339,6 +1339,6 @@ None of this manual process is necessary in Scala.
 [modeling-intro]: {% link _overviews/scala3-book/domain-modeling-intro.md %}
 [multiversal]: {% link _overviews/scala3-book/ca-multiversal-equality.md %}
 [toplevel]: {% link _overviews/scala3-book/taste-toplevel-definitions.md %}
-[type-classes]: {% link _overviews/scala3-book/types-type-classes.md %}
+[type-classes]: {% link _overviews/scala3-book/ca-type-classes.md %}
 [union-types]: {% link _overviews/scala3-book/types-union.md %}
 </div>
diff --git a/_overviews/scala3-book/scala-tools.md b/_overviews/scala3-book/scala-tools.md
@@ -3,7 +3,7 @@ title: Scala Tools
 type: chapter
 description: This chapter looks at two commonly-used Scala tools, sbt and ScalaTest.
 languages: [zh-cn]
-num: 69
+num: 68
 previous-page: concurrency
 next-page: tools-sbt
 ---
diff --git a/_overviews/scala3-book/tools-sbt.md b/_overviews/scala3-book/tools-sbt.md
@@ -3,7 +3,7 @@ title: Building and Testing Scala Projects with sbt
 type: section
 description: This section looks at a commonly-used build tool, sbt, and a testing library, ScalaTest.
 languages: [zh-cn]
-num: 70
+num: 69
 previous-page: scala-tools
 next-page: tools-worksheets
 ---
diff --git a/_overviews/scala3-book/tools-worksheets.md b/_overviews/scala3-book/tools-worksheets.md
@@ -3,7 +3,7 @@ title: Worksheets
 type: section
 description: This section looks at worksheets, an alternative to Scala projects.
 languages: [zh-cn]
-num: 71
+num: 70
 previous-page: tools-sbt
 next-page: interacting-with-java
 ---
diff --git a/_overviews/scala3-book/types-type-classes.md b/_overviews/scala3-book/types-type-classes.md
diff --git a/_overviews/scala3-book/where-next.md b/_overviews/scala3-book/where-next.md
@@ -3,9 +3,9 @@ title: Where To Go Next
 type: chapter
 description: Where to go next after reading the Scala Book
 languages: [zh-cn]
-num: 76
+num: 75
 previous-page: scala-for-python-devs
-next-page:
+next-page: 
 ---
 
 We hope you enjoyed this introduction to the Scala programming language, and we also hope we were able to share some of the beauty of the language.
