diff --git a/_overviews/scala3-book/taste-methods.md b/_overviews/scala3-book/taste-methods.md index 6f6012d856..1c98771ad0 100644 --- a/_overviews/scala3-book/taste-methods.md +++ b/_overviews/scala3-book/taste-methods.md @@ -14,99 +14,120 @@ next-page: taste-functions Scala classes, case classes, traits, enums, and objects can all contain methods. The syntax of a simple method looks like this: +{% tabs method_1 %} +{% tab 'Scala 2 and 3' for=method_1 %} ```scala def methodName(param1: Type1, param2: Type2): ReturnType = // the method body // goes here ``` +{% endtab %} +{% endtabs %} Here are a few examples: +{% tabs method_2 %} +{% tab 'Scala 2 and 3' for=method_2 %} ```scala def sum(a: Int, b: Int): Int = a + b def concatenate(s1: String, s2: String): String = s1 + s2 ``` +{% endtab %} +{% endtabs %} You don’t have to declare a method’s return type, so you can write those methods like this, if you prefer: +{% tabs method_3 %} +{% tab 'Scala 2 and 3' for=method_3 %} ```scala def sum(a: Int, b: Int) = a + b def concatenate(s1: String, s2: String) = s1 + s2 ``` +{% endtab %} +{% endtabs %} This is how you call those methods: +{% tabs method_4 %} +{% tab 'Scala 2 and 3' for=method_4 %} ```scala val x = sum(1, 2) val y = concatenate("foo", "bar") ``` +{% endtab %} +{% endtabs %} Here’s an example of a multiline method: +{% tabs method_5 class=tabs-scala-version %} +{% tab 'Scala 2' for=method_5 %} +```scala +def getStackTraceAsString(t: Throwable): String = { + val sw = new StringWriter + t.printStackTrace(new PrintWriter(sw)) + sw.toString +} +``` +{% endtab %} + +{% tab 'Scala 3' for=method_5 %} ```scala def getStackTraceAsString(t: Throwable): String = val sw = new StringWriter t.printStackTrace(new PrintWriter(sw)) sw.toString ``` +{% endtab %} +{% endtabs %} Method parameters can also have default values. In this example, the `timeout` parameter has a default value of `5000`: +{% tabs method_6 %} +{% tab 'Scala 2 and 3' for=method_6 %} ```scala def makeConnection(url: String, timeout: Int = 5000): Unit = println(s"url=$url, timeout=$timeout") ``` +{% endtab %} +{% endtabs %} Because a default `timeout` value is supplied in the method declaration, the method can be called in these two ways: +{% tabs method_7 %} +{% tab 'Scala 2 and 3' for=method_7 %} ```scala makeConnection("https://localhost") // url=http://localhost, timeout=5000 makeConnection("https://localhost", 2500) // url=http://localhost, timeout=2500 ``` +{% endtab %} +{% endtabs %} Scala also supports the use of _named parameters_ when calling a method, so you can also call that method like this, if you prefer: +{% tabs method_8 %} +{% tab 'Scala 2 and 3' for=method_8 %} ```scala makeConnection( url = "https://localhost", timeout = 2500 ) ``` +{% endtab %} +{% endtabs %} Named parameters are particularly useful when multiple method parameters have the same type. At a glance, with this method you may wonder which parameters are set to `true` or `false`: -```scala -engage(true, true, true, false) -``` - -Without help from an IDE that code can be hard to read, but this code is much more obvious: +{% tabs method_9 %} +{% tab 'Scala 2 and 3' for=method_9 %} ```scala -engage( - speedIsSet = true, - directionIsSet = true, - picardSaidMakeItSo = true, - turnedOffParkingBrake = false -) +engage(true, true, true, false) ``` - - -## Extension methods - -_Extension methods_ let you add new methods to closed classes. -For instance, if you want to add two methods named `hello` and `aloha` to the `String` class, declare them as extension methods: - -```scala -extension (s: String) - def hello: String = s"Hello, ${s.capitalize}!" - def aloha: String = s"Aloha, ${s.capitalize}!" - -"world".hello // "Hello, World!" -"friend".aloha // "Aloha, Friend!" -``` +{% endtab %} +{% endtabs %} The `extension` keyword declares that you’re about to define one or more extension methods on the parameter that’s put in parentheses. As shown with this example, the parameter `s` of type `String` can then be used in the body of your extension methods. @@ -115,6 +136,9 @@ This next example shows how to add a `makeInt` method to the `String` class. Here, `makeInt` takes a parameter named `radix`. The code doesn’t account for possible string-to-integer conversion errors, but skipping that detail, the examples show how it works: +{% tabs extension_2 class=tabs-scala-version %} +{% tab 'Scala 3 Only' for=extension_2 %} + ```scala extension (s: String) def makeInt(radix: Int): Int = Integer.parseInt(s, radix) @@ -124,13 +148,12 @@ extension (s: String) "100".makeInt(2) // Int = 4 ``` - +{% endtab %} +{% endtabs %} ## See also Scala Methods can be much more powerful: they can take type parameters and context parameters. They are covered in detail in the [Domain Modeling][data-1] section. - - [data-1]: {% link _overviews/scala3-book/domain-modeling-tools.md %}