CODEWITHSUNDEEP
pythonscalafluentchaining
Hugh Pearse
Hugh Pearse

Reputation: 729

Scala method chaining - hello world

I'm currently learning method chaining. I've provided a working python example.

#!/bin/python3
import sys

class Generator(object):

    def __init__(self):
        return None

    def echo(self, myStr):
        sys.stdout.write(myStr)
        return self

g = Generator()
g.echo("Hello, ").echo("World!\n")

But the Scala version doesn't seem to work, no text is being output. 

#!/usr/bin/env scala

final class Printer() {
  def echo(msg: String): this.type = {
    println(msg)
    this
  }
}

class Driver {
  def main(args: Array[String]) {
    var pr = new Printer();
    pr.echo("Hello, ").echo("World!")
  }
}

Does anybody know why the scala version is not working and why?

Upvotes: 0

Views: 1521

Answers (2)

zwer
zwer

Reputation: 25779

You need to compile and call your scala bytecode aferwards. Also, you don't need to specify this.type if your Printer is final, e.g. if your driver.scala file contains:

final class Printer() {
  def echo(msg: String) = {
    println(msg)
    this
  }
}

object Driver {
   def main(args: Array[String]) {
        var pr = new Printer();
        pr.echo("Hello, ").echo("World!")
   }
}

Then just call:

scalac driver.scala
scala Driver

Upvotes: 3

Hyun Min Choi
Hyun Min Choi

Reputation: 49

You should call the main method in your script.

new Driver().main(...) should solve your problem.

Besides, it is the norm to define a main method in an object.

So, instead of 

class Driver {
  def main(args: Array[String]) {
    var pr = new Printer();
    pr.echo("Hello, ").echo("World!")
  }
}

new Driver().main(...)

I would recommend the following.

object Driver {
  def main(args: Array[String]) {
    var pr = new Printer();
    pr.echo("Hello, ").echo("World!")
  }
}

Driver.main(...)

Good luck!

Upvotes: 0

Related Questions