Scala Programming Projects

By-name parameters

We can go a bit further and delay the evaluation of function arguments. A by-name parameter is like a function that does not take any argument. This way, it only gets evaluated when the function's body requires it.

Say that you have an application that loads its configuration from a file or a database. You want the application to start as fast as possible, and so you decide to use lazy val to load a greeting message on demand, as shown in the following code:

object AppConfig {
  lazy val greeting: String = {
    println("Loading greeting")
    "Hello "
  }
}

Note that for the sake of brevity we haven't actually loaded anything here—just imagine that we did.

If we then want to use the greeting variable in a function but keep delaying ...