Strictness and laziness

Scala's default evaluation strategy is strict. This means that if you don't do anything special, any variable declaration or arguments of a function call are immediately evaluated. The opposite of a strict evaluation strategy is a lazy evaluation strategy, which means that evaluation is performed only when needed.

Strict val

The following is a strict variable declaration:

class StrictDemo {
  val strictVal = {
    println("Evaluating strictVal")
    "Hello"
  }
}
val strictDemo = new StrictDemo
//Evaluating strictVal
//strictDemo: StrictDemo = StrictDemo@32fac009

We can see that println is called immediately. This means that the block at the right side of the assignment...