26 Feb 2021 Use Scala's asInstanceOf method to cast an instance to the desired type. In the following example, the object returned by the lookup method is

2010-05-19

Here it is required to know two important method of Scala, which are used in the following example. obj.isInstanceOf [Point] To check Type of obj and Point are same are not. obj.asInstanceOf [Point] means exact casting by taking the object obj type and returns the same obj as Point type. Try the following example program to implement traits. Example Below is the source for the reduceLeft method of Scala's TraversableOnce trait. What is happening with the line that reads var acc: B = 0.asInstanceOf[B]?. To me, it seems that if I call this on a list of Strings, such as List("a", "b", "c"), this would result in something like 0.asInstanceOf[String].

And neither does null.asInstanceOf [Double], null.asInstanceOf [Boolean], null.asInstanceOf [Char] . PS: My scala library is of version 2.9.0.1 and OS windows XP. scala nullpointerexception. Scala: Convert a csv string to Array. arrays,string,scala,split,scala-collections.

isInstanceOf[String]).map(_.asInstanceOf[String]) res6: List[String] = List(one, three) // finally it works scala> res6.foreach(x => println(x.length()))

StringColumnExtensionMethods[P1] AnyVal Expansion tree term for weak quantifiers instances. Source: terms.scala. Linear Supertypes.

asInstanceOf [T ] returns the “null” object itself if T conforms to scala.AnyRef, and throws a NullPointerException otherwise And neither does null.asInstanceOf [Double], null.asInstanceOf [Boolean], null.asInstanceOf [Char]. PS: My scala library is of version 2.9.0.1 and OS windows XP

Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not.

C++, D, Rust etc.) All of the interop APIs discussed here are defined in scala.scalanative.native package. For brevity, we’re going to refer to that namespace as just native. Sometimes it is necessary to express that the type of an object is a subtype of several other types. In Scala this can be expressed with the help of compound types, which are intersections of object types. scala – isInstanceOf , asInstanceOf November 10, 2016 November 10, 2016 corerootz - Ravi Kiran Krovvidi Scala scala isinstanceof asinstanceof To test whether an expression expr has type String, say, you write: Based on a concrete example with Scala, Spring and JPA the article explains how to enhance Spring with Scala’s powerful concepts such as implicit conversions and traits.
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This includes C and other languages that can expose APIs via C ABI (e.g. C++, D, Rust etc.) All of the interop APIs discussed here are defined in scala.scalanative.native package. For brevity, we’re going to refer to that namespace as just native.

We would like a type-safe implementation that requires only one container class implementation. This is the purpose of Scala generics.
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That is why the asInstanceOf is used in the above sample. When using non-blocking it is better to use the mapTo method to safely try to cast a Future to an expected type: import scala.concurrent.Future import akka.pattern.ask val future : Future [ String ] = ask ( actor , msg ). mapTo [ String ]

The asInstanceOf method is defined in the Scala Any class and is therefore available on all objects. The first is a String and the rest are numbers (either Int or Double) so I am using Any* to get the arguments. I would like to treat the numbers uniformly as Doubles, but I cannot just use asInstanceOf[Double] on the numeric arguments. For example: val arr = Array("varargs list of numbers", 3, 4.2, 5) val d = arr(1).asInstanceOf[Double] gives: Discussion As shown, a match expression lets you match multiple types, so using it to replace the isInstanceOf method is just a natural use of the case syntax and the general pattern-matching approach used in Scala applications.

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2018年12月17日 Ø 注意：如果物件是null，則isInstanceOf 一定返回false， asInstanceOf 一定返回 null；. Ø Scala與Java型別檢查和轉換Scala Java obj.

Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. I was doing a little Scala programming this morning, and because I hadn't written any code in a while, I managed to forget how isInstanceOf works with inheritance in Scala. To refresh my memory, I wrote the following example code: /** * The problem with Scala isInstanceOf and inheritance.