scala cookbook

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 13.9, “Simple concurrency with Scala Futures.”

Problem

You want a simple way to run one or more tasks concurrently in a Scala application, including a way to handle their results when the tasks finish. For instance, you may want to make several web service calls in parallel, and then work with their results after they all return.

Solution

A Future gives you a simple way to run an algorithm concurrently. A future starts running concurrently when you create it and returns a result at some point, well, in the future. In Scala, it’s said that a future returns “eventually.”

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 14.6, “How to disassemble and decompile Scala code.”

Problem

In the process of learning Scala, or trying to understand a particular problem, you want to examine the source code and bytecode the Scala compiler generates from your original source code.

Solution

You can use several different approaches to see how your Scala source code is translated:

Scala problem: You want to define an equals method for your class so you can compare object instances to each other.

Solution

If you’re new to Scala, a first thing to know is that object instances are compared with ==:

"foo" == "foo"   // true
"foo" == "bar"   // false
"foo" == null    // false
null == "foo"    // false
1 == 1           // true
1 == 2           // false
1d == 1.0d       // true

case class Person(name: String)
Person("Jess") == Person("Jessie")   // false

This is different than Java, which uses == for primitive values and equals for object comparisons.