Scala - Revision history

PeterHarding at 09:51, 2 March 2026

2026-03-02T09:51:47Z

← Older revision		Revision as of 19:51, 2 March 2026
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	=Scala Notes=		= Scala Notes =

	* https://en.wikipedia.org/wiki/Scala_(programming_language)		* https://en.wikipedia.org/wiki/Scala_(programming_language)

PeterHarding at 23:49, 12 May 2021

2021-05-12T23:49:10Z

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PeterHarding at 23:30, 12 May 2021

2021-05-12T23:30:08Z

@@ Line 61: / Line 61: @@
 ==Default initializer==
   var x: String = _   // unloved syntax may be eliminated
 [[Category:Scala]]

PeterHarding at 23:22, 12 May 2021

2021-05-12T23:22:29Z

← Older revision		Revision as of 09:22, 13 May 2021
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	* https://en.wikipedia.org/wiki/Scala_(programming_language)		* https://en.wikipedia.org/wiki/Scala_(programming_language)

			= Use of '_' =

			From - https://stackoverflow.com/questions/8000903/what-are-all-the-uses-of-an-underscore-in-scala

			<pre>
			import scala._ // Wild card -- all of Scala is imported
			import scala.{ Predef => _, _ } // Exception, everything except Predef
			def f[M[_]] // Higher kinded type parameter
			def f(m: M[_]) // Existential type
			_ + _ // Anonymous function placeholder parameter
			m _ // Eta expansion of method into method value
			m(_) // Partial function application
			_ => 5 // Discarded parameter
			case _ => // Wild card pattern -- matches anything
			val (a, _) = (1, 2) // same thing
			for (_ <- 1 to 10) // same thing
			f(xs: _) // Sequence xs is passed as multiple parameters to f(ys: T)
			case Seq(xs @ _*) // Identifier xs is bound to the whole matched sequence
			var i: Int = _ // Initialization to the default value
			def abc_<>! // An underscore must separate alphanumerics from symbols on identifiers
			t._2 // Part of a method name, such as tuple getters
			1_000_000 // Numeric literal separator (Scala 2.13+)
			</pre>

			So...

			==Existential types==
			def foo(l: List[Option[_]]) = ...
			==Higher kinded type parameters==
			case class A[K[_],T](a: K[T])
			==Ignored variables==
			val _ = 5
			==Ignored parameters==
			List(1, 2, 3) foreach { _ => println("Hi") }
			==Ignored names of self types==
			trait MySeq { _: Seq[_] => }
			==Wildcard patterns==
			Some(5) match { case Some(_) => println("Yes") }
			==Wildcard patterns in interpolations==
			"abc" match { case s"a$_c" => }
			==Sequence wildcard in patterns==
			C(1, 2, 3) match { case C(vs @ _*) => vs.foreach(f(_)) }
			==Wildcard imports==
			import java.util._
			==Hiding imports==
			import java.util.{ArrayList => _, _}
			==Joining letters to operators==
			def bang_!(x: Int) = 5
			==Assignment operators==
			def foo_=(x: Int) { ... }
			==Placeholder syntax==
			List(1, 2, 3) map (_ + 2)
			==Method values==
			List(1, 2, 3) foreach println _
			==Converting call-by-name parameters to functions==
			def toFunction(callByName: => Int): () => Int = callByName _
			==Default initializer==
			var x: String = _ // unloved syntax may be eliminated

	[[Category:Scala]]		[[Category:Scala]]

PeterHarding: Created page with "=Scala Notes= * https://en.wikipedia.org/wiki/Scala_(programming_language) Category:Scala"

2021-04-14T23:18:23Z

Created page with "=Scala Notes= * https://en.wikipedia.org/wiki/Scala_(programming_language) Category:Scala"

New page

=Scala Notes=

* https://en.wikipedia.org/wiki/Scala_(programming_language)

[[Category:Scala]]