Geek asks and answers

Scala style: how many nest functions?

One of the advantages of Scala is that it gives you great control over the area. You can invest performs the following functions:

def fn1 = {
  def fn11 = {
    ...
  }
  def fn12 = {
    ...
    def fn121 = {
      ...
    }
  }
  ...
  def fn13 = {
    ...
  }
}

The problem here is that fn1 might start to look a little intimidating. Based on the Java background, we recommend that you keep the functions small enough so that they can be viewed on a single "page" in the IDE.

What do you think about taking fn12 from fn1 based on your reasoning: "It is only used in fn1 right now, but it may be useful somewhere else in the class later ..."

Also, do you have any preferences regarding the placement of nested functions - before or after the code that calls them?

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def callsRecursive(p: Param): Result = {
  def recursive(p: Param, o: OtherParam, pr: PartialResult = default): Result = {
    ...
  }
}

-:

def doesGraphics(p: Point) {
  def up(p: Point): Point = // ...
  def dn(p: Point): Point = // ...
  def lf(p: Point): Point = // ...
  def rt(p: Point): Point = // ...
  /* Lots of turtle-style drawing */
}

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private[scope] def fn12 = { ... }

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I personally avoid nesting of the named methods ( def), while I am not against nested anonymous functions (for example, closures in programming a continuation style).

0
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Nested functions are useful (e.g. recursion helpers). But if they become too numerous, there is nothing that will prevent you from extracting them into a new type and delegating to it.

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