Merge pull request #3126 from gkepka/scala-book-control-structures

Scala 2 Book migration - Control Structures
scala · Dec 10, 2024 · 70efd3e · 70efd3e
2 parents c35f5df + e803479
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diff --git a/_overviews/scala3-book/ca-context-bounds.md b/_overviews/scala3-book/ca-context-bounds.md
@@ -3,7 +3,7 @@ title: Context Bounds
 type: section
 description: This page demonstrates Context Bounds in Scala.
 languages: [ru, zh-cn]
-num: 62
+num: 63
 previous-page: ca-context-parameters
 next-page: ca-given-imports
 ---

diff --git a/_overviews/scala3-book/ca-context-parameters.md b/_overviews/scala3-book/ca-context-parameters.md
@@ -3,7 +3,7 @@ title: Context Parameters
 type: section
 description: This page demonstrates how to declare context parameters, and how the compiler infers them at call-site.
 languages: [ru, zh-cn]
-num: 61
+num: 62
 previous-page: ca-extension-methods
 next-page: ca-context-bounds
 redirect_from: /scala3/book/ca-given-using-clauses.html

diff --git a/_overviews/scala3-book/ca-contextual-abstractions-intro.md b/_overviews/scala3-book/ca-contextual-abstractions-intro.md
@@ -3,7 +3,7 @@ title: Contextual Abstractions
 type: chapter
 description: This chapter provides an introduction to the Scala 3 concept of Contextual Abstractions.
 languages: [ru, zh-cn]
-num: 59
+num: 60
 previous-page: types-others
 next-page: ca-extension-methods
 ---

diff --git a/_overviews/scala3-book/ca-extension-methods.md b/_overviews/scala3-book/ca-extension-methods.md
@@ -3,7 +3,7 @@ title: Extension Methods
 type: section
 description: This page demonstrates how Extension Methods work in Scala 3.
 languages: [ru, zh-cn]
-num: 60
+num: 61
 previous-page: ca-contextual-abstractions-intro
 next-page: ca-context-parameters
 scala3: true

diff --git a/_overviews/scala3-book/ca-given-imports.md b/_overviews/scala3-book/ca-given-imports.md
@@ -3,7 +3,7 @@ title: Given Imports
 type: section
 description: This page demonstrates how 'given' import statements work in Scala 3.
 languages: [ru, zh-cn]
-num: 63
+num: 64
 previous-page: ca-context-bounds
 next-page: ca-type-classes
 scala3: true

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.
 languages: [ru, zh-cn]
-num: 66
+num: 67
 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: [ru, zh-cn]
-num: 65
+num: 66
 previous-page: ca-type-classes
 next-page: ca-implicit-conversions
 scala3: true

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: [ru, zh-cn]
-num: 67
+num: 68
 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
@@ -3,7 +3,7 @@ title: Type Classes
 type: section
 description: This page demonstrates how to create and use type classes.
 languages: [ru, zh-cn]
-num: 64
+num: 65
 previous-page: ca-given-imports
 next-page: ca-multiversal-equality
 redirect_from: /scala3/book/types-type-classes.html

diff --git a/_overviews/scala3-book/collections-classes.md b/_overviews/scala3-book/collections-classes.md
@@ -3,7 +3,7 @@ title: Collections Types
 type: section
 description: This page introduces the common Scala 3 collections types and some of their methods.
 languages: [ru, zh-cn]
-num: 38
+num: 39
 previous-page: collections-intro
 next-page: collections-methods
 ---

diff --git a/_overviews/scala3-book/collections-intro.md b/_overviews/scala3-book/collections-intro.md
@@ -3,7 +3,7 @@ title: Scala Collections
 type: chapter
 description: This page provides and introduction to the common collections classes and their methods in Scala 3.
 languages: [ru, zh-cn]
-num: 37
+num: 38
 previous-page: packaging-imports
 next-page: collections-classes
 ---

diff --git a/_overviews/scala3-book/collections-methods.md b/_overviews/scala3-book/collections-methods.md
@@ -3,7 +3,7 @@ title: Collections Methods
 type: section
 description: This page demonstrates the common methods on the Scala 3 collections classes.
 languages: [ru, zh-cn]
-num: 39
+num: 40
 previous-page: collections-classes
 next-page: collections-summary
 ---

diff --git a/_overviews/scala3-book/collections-summary.md b/_overviews/scala3-book/collections-summary.md
@@ -3,7 +3,7 @@ title: Summary
 type: section
 description: This page provides a summary of the Collections chapter.
 languages: [ru, zh-cn]
-num: 40
+num: 41
 previous-page: collections-methods
 next-page: fp-intro
 ---

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: [ru, zh-cn]
-num: 68
+num: 69
 previous-page: ca-summary
 next-page: scala-tools
 ---

diff --git a/_overviews/scala3-book/control-structures.md b/_overviews/scala3-book/control-structures.md
@@ -812,7 +812,7 @@ speak(Person("Bam Bam"))   // "Bam Bam says, Bam bam!"
 
 #### Binding matched patterns to variables
 
-You can bind the matched pattern to a variable to use type-specific behavior.
+You can bind the matched pattern to a variable to use type-specific behavior:
 
 {% tabs pattern-binding class=tabs-scala-version %}
 {% tab 'Scala 2' for=pattern-binding %}
@@ -992,10 +992,68 @@ def pattern(x: Matchable): String = x match
 {% endtab %}
 {% endtabs %}
 
-{% comment %}
-TODO: Add in the new Scala 3 syntax shown on this page:
-http://dotty.epfl.ch/docs/reference/changed-features/match-syntax.html
-{% endcomment %}
+You can also write the code on the right side of the `=>` on multiple lines if you think it is easier to read. Here is one example:
+
+{% tabs control-structures-31 class=tabs-scala-version %}
+{% tab 'Scala 2' for=control-structures-31 %}
+```scala
+count match {
+  case 1 =>
+    println("one, a lonely number")
+  case x if x == 2 || x == 3 => 
+    println("two's company, three's a crowd")
+  case x if x > 3 =>
+    println("4+, that's a party")
+  case _ => 
+    println("i'm guessing your number is zero or less")
+}
+```
+{% endtab %}
+{% tab 'Scala 3' for=control-structures-31 %}
+```scala
+count match
+  case 1 => 
+    println("one, a lonely number")
+  case x if x == 2 || x == 3 => 
+    println("two's company, three's a crowd")
+  case x if x > 3 => 
+    println("4+, that's a party")
+  case _ => 
+    println("i'm guessing your number is zero or less")
+```
+{% endtab %}
+{% endtabs %}
+
+In Scala 3, `match` expressions can be chained:
+
+{% tabs 'control-structures-32' %}
+{% tab 'Scala 3 Only' %}
+```scala
+i match
+  case odd: Int if odd % 2 == 1 => "odd"
+  case even: Int if even % 2 == 0 => "even"
+  case _ => "not an integer"
+match
+  case "even" => true
+  case _ => false
+```
+{% endtab %}
+{% endtabs %}
+
+The `match` expression can also follow a period, which simplifies matching on results returned by chained method calls:
+
+{% tabs 'control-structures-33' %}
+{% tab 'Scala 3 Only' %}
+```scala
+List(1, 2, 3)
+  .map(_ * 2)
+  .headOption
+  .match
+    case Some(value) => println(s"The head is: $value")
+    case None => println("The list is empty")
+```
+{% endtab %}
+{% endtabs %}
 
 ## try/catch/finally
 
@@ -1004,8 +1062,8 @@ For consistency, Scala uses the same syntax that `match` expressions use and sup
 
 In the following example, `openAndReadAFile` is a method that does what its name implies: it opens a file and reads the text in it, assigning the result to the mutable variable `text`:
 
-{% tabs control-structures-31 class=tabs-scala-version %}
-{% tab 'Scala 2' for=control-structures-31 %}
+{% tabs control-structures-34 class=tabs-scala-version %}
+{% tab 'Scala 2' for=control-structures-34 %}
 ```scala
 var text = ""
 try {
@@ -1019,7 +1077,7 @@ try {
 }
 ```
 {% endtab %}
-{% tab 'Scala 3' for=control-structures-31 %}
+{% tab 'Scala 3' for=control-structures-34 %}
 ```scala
 var text = ""
 try

diff --git a/_overviews/scala3-book/fun-eta-expansion.md b/_overviews/scala3-book/fun-eta-expansion.md
@@ -3,7 +3,7 @@ title: Eta-Expansion
 type: section
 description: This page discusses Eta-Expansion, the Scala technology that automatically and transparently converts methods into functions.
 languages: [ru, zh-cn]
-num: 31
+num: 32
 previous-page: fun-function-variables
 next-page: fun-hofs
 ---

diff --git a/_overviews/scala3-book/fun-function-variables.md b/_overviews/scala3-book/fun-function-variables.md
@@ -5,7 +5,7 @@ description: This page shows how to use function variables in Scala.
 languages: [ru, zh-cn]
 num: 30
 previous-page: fun-anonymous-functions
-next-page: fun-eta-expansion
+next-page: fun-partial-functions
 ---
 
 

diff --git a/_overviews/scala3-book/fun-hofs.md b/_overviews/scala3-book/fun-hofs.md
@@ -3,7 +3,7 @@ title: Higher-Order Functions
 type: section
 description: This page demonstrates how to create and use higher-order functions in Scala.
 languages: [ru, zh-cn]
-num: 32
+num: 33
 previous-page: fun-eta-expansion
 next-page: fun-write-map-function
 ---

diff --git a/_overviews/scala3-book/fun-intro.md b/_overviews/scala3-book/fun-intro.md
@@ -10,5 +10,5 @@ next-page: fun-anonymous-functions
 
 
 Where the previous chapter introduced Scala *methods*, this chapter digs into *functions*.
-The topics that are covered include anonymous functions, function variables, and higher-order functions (HOFs), including how to create your own HOFs.
+The topics that are covered include anonymous functions, partial functions, function variables, and higher-order functions (HOFs), including how to create your own HOFs.
 
diff --git a/_overviews/scala3-book/fun-partial-functions.md b/_overviews/scala3-book/fun-partial-functions.md
@@ -0,0 +1,81 @@
+---
+title: Partial Functions
+type: section
+description: This page shows how to use partial functions in Scala.
+num: 31
+previous-page: fun-function-variables
+next-page: fun-eta-expansion
+---
+
+A partial function is a function that may not be defined for all values of its argument type. In Scala, partial functions
+are unary functions implementing the `PartialFunction[A, B]` trait, where `A` is the argument type and `B` the result type.
+
+To define a partial function, use a `case` identical to those used in `match` expressions:
+
+{% tabs fun-partial-1 %}
+{% tab 'Scala 2 and 3' %}
+```scala
+val doubledOdds: PartialFunction[Int, Int] = {
+  case i if i % 2 == 1 => i * 2
+}
+```
+{% endtab %}
+{% endtabs %}
+
+To check if a partial function is defined for an argument, use the `isDefinedAt` method:
+
+{% tabs fun-partial-2 %}
+{% tab 'Scala 2 and 3' %}
+```scala
+doubledOdds.isDefinedAt(3)  // true
+doubledOdds.isDefinedAt(4)  // false
+```
+{% endtab %}
+{% endtabs %}
+
+Trying to apply a partial function to an argument not belonging to its domain results in `MatchError`:
+
+{% tabs fun-partial-3 %}
+{% tab 'Scala 2 and 3' %}
+```scala
+doubledOdds(4)  // Exception in thread "main" scala.MatchError: 4
+```
+{% endtab %}
+{% endtabs %}
+
+### Using partial functions
+
+A partial function can be passed as an argument to a method:
+
+{% tabs fun-partial-4 %}
+{% tab 'Scala 2 and 3' %}
+```scala
+val res = List(1, 2, 3).collect({ case i if i % 2 == 1 => i * 2 }) // List(2, 6)
+```
+{% endtab %}
+{% endtabs %}
+
+You can define a default value for arguments not in domain with `applyOrElse`:
+
+{% tabs fun-partial-5 %}
+{% tab 'Scala 2 and 3' %}
+```scala
+doubledOdds.applyOrElse(4, _ + 1)  // 5
+```
+{% endtab %}
+{% endtabs %}
+
+Two partial function can be composed with `orElse`, the second function will be applied for arguments where the first
+one is not defined:
+
+{% tabs fun-partial-6 %}
+{% tab 'Scala 2 and 3' %}
+```scala
+val incrementedEvens: PartialFunction[Int, Int] = {
+  case i if i % 2 == 0 => i + 1
+}
+
+val res2 = List(1, 2, 3).collect(doubledOdds.orElse(incrementedEvens)) // List(2, 3, 6)
+```
+{% endtab %}
+{% endtabs %}
diff --git a/_overviews/scala3-book/fun-summary.md b/_overviews/scala3-book/fun-summary.md
@@ -3,7 +3,7 @@ title: Summary
 type: section
 description: This page provides a summary of the previous 'Functions' sections.
 languages: [ru, zh-cn]
-num: 35
+num: 36
 previous-page: fun-write-method-returns-function
 next-page: packaging-imports
 ---

diff --git a/_overviews/scala3-book/fun-write-map-function.md b/_overviews/scala3-book/fun-write-map-function.md
@@ -3,7 +3,7 @@ title: Write Your Own map Method
 type: section
 description: This page demonstrates how to create and use higher-order functions in Scala.
 languages: [ru, zh-cn]
-num: 33
+num: 34
 previous-page: fun-hofs
 next-page: fun-write-method-returns-function
 ---

diff --git a/_overviews/scala3-book/fun-write-method-returns-function.md b/_overviews/scala3-book/fun-write-method-returns-function.md
@@ -3,7 +3,7 @@ title: Creating a Method That Returns a Function
 type: section
 description: This page demonstrates how to create and use higher-order functions in Scala.
 languages: [ru, zh-cn]
-num: 34
+num: 35
 previous-page: fun-write-map-function
 next-page: fun-summary
 ---

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: [ru, zh-cn]
-num: 72
+num: 73
 previous-page: tools-worksheets
 next-page: scala-for-java-devs
 ---

diff --git a/_overviews/scala3-book/packaging-imports.md b/_overviews/scala3-book/packaging-imports.md
@@ -3,7 +3,7 @@ title: Packaging and Imports
 type: chapter
 description: A discussion of using packages and imports to organize your code, build related modules of code, control scope, and help prevent namespace collisions.
 languages: [ru, zh-cn]
-num: 36
+num: 37
 previous-page: fun-summary
 next-page: collections-intro
 ---

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: 74
 previous-page: interacting-with-java
 next-page: scala-for-javascript-devs
 ---
Original file line number	Diff line number	Diff line change
Expand Up		@@ -10,5 +10,5 @@ next-page: fun-anonymous-functions


		Where the previous chapter introduced Scala methods, this chapter digs into functions.
		The topics that are covered include anonymous functions, function variables, and higher-order functions (HOFs), including how to create your own HOFs.
		The topics that are covered include anonymous functions, partial functions, function variables, and higher-order functions (HOFs), including how to create your own HOFs.