Scala test

colon_colon.md

• ref

  • http://stackoverflow.com/questions/16712328/why-does-a-list-report-error-is-not-member-of-string

• example

  scala> def foo(s: String*) = for ( i <- s ) println(i)
  foo: (s: String*)Unit
  
  scala> val l: List[String] = List("c", "d")
  l: List[String] = List(c, d)
  
  scala> foo(("a" :: "b" :: l): _*)
  a
  b
  c
  d

div.md

❯ scala
Welcome to Scala 2.12.8 (OpenJDK 64-Bit Server VM, Java 1.8.0_192).
Type in expressions for evaluation. Or try :help.

scala> import scala.util.Try
import scala.util.Try

scala> def div(s1: Option[String], s2: Option[String]): Option[Int] = {
     |   for {
     |     a <- Try(s1.map(_.toInt)).toOption
     |     b <- Try(s2.map(_.toInt)).toOption
     |     l <- a
     |     r <- b if r != 0
     |     res = l / r
     |   } yield res
     | }
div: (s1: Option[String], s2: Option[String])Option[Int]

scala> div(Some("1"), Some("2"))
res1: Option[Int] = Some(0)

scala> div(Some("1"), Some("0"))
res2: Option[Int] = None

scala> div(Some("1"), Some("0.1"))
res3: Option[Int] = None

scala> div(Some("1"), Some("100"))
res4: Option[Int] = Some(0)

scala> div(Some("1000"), Some("100"))
res5: Option[Int] = Some(10)

prefer_def_over_val_for_contant.md

• https://twitter.com/not_xuwei_k/status/1328535431642804226/photo/1

• test

  ❯ cat A.scala B.scala
  class A {
    val b = 10L
  }
  class B {
    def b = 10L
  }
  
  ❯ javap -c A
  Compiled from "A.scala"
  public class A {
    public long b();
      Code:
         0: aload_0
         1: getfield      #13                 // Field b:J
         4: lreturn
  
    public A();
      Code:
         0: aload_0
         1: invokespecial #19                 // Method java/lang/Object."<init>":()V
         4: aload_0
         5: ldc2_w        #20                 // long 10l
         8: putfield      #13                 // Field b:J
        11: return
  }
  
  ❯ javap -c B
  Compiled from "B.scala"
  public class B {
    public long b();
      Code:
         0: ldc2_w        #11                 // long 10l
         3: lreturn
  
    public B();
      Code:
         0: aload_0
         1: invokespecial #18                 // Method java/lang/Object."<init>":()V
         4: return
  }