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Nesting Depth

Nesting depth is the maximum number of nested control/scope constructs you must mentally “hold” while reading a function. Deeper nesting increases cognitive load and the risk of bugs. Flattening (early returns, guard clauses, small helpers) usually improves readability and testability. Read more in WikiPedia.

What it Measures

Deepest level of nested blocks/branches. Highly nested code is harder to read and maintain.

How it's Measured

  • Counts depth for:
    • Blocks: {}
    • Conditionals: if (...) else (...)
    • Pattern matching: each case body
    • Loops: while, do ... while, for, for ... yield
    • Exception handling: try body, each catch case body, and finally body
    • Anonymous functions: the lambda body

Why it Helps

Highlights places to flatten control flow (early returns, small helpers).

Readability and Guard Clauses

Deep indentation increases the cognitive load because the reader must hold multiple active contexts in mind. Every extra level is another state to track. The aim isn’t “no nesting ever,” it’s to keep local depth small so each unit of code is quick to scan. Shallow functions are easier to review, easier to test, and easier to evolve.

1. From pyramid to guard clauses Depth: 4 → 1–2

Each if opens a new level, pushing the happy path deeper and deeper. Readers now have to match three braces and remember which failure corresponds to which check. Bugs often creep in when you add a fourth condition and forget to update the right branch. Guard clauses front‑load failure and keep the success path flush-left. The function’s visual shape now communicates intent: handle the edge cases, then proceed. Complexity hasn’t changed much, but perceived complexity drops dramatically.

def process(u: User): Either[String, Receipt] = {
  if (u != null) {
    if (u.active) {
      if (u.cart.nonEmpty) {
        Right(checkout(u.cart))
      } else Left("empty cart")
    } else Left("inactive")
  } else Left("no user")
}

def process(u: User): Either[String, Receipt] = {
  if (u == null) Left("no user")
  if (!u.active) Left("inactive")
  if (u.cart.isEmpty) Left("empty cart")
  Right(checkout(u.cart))
}

Tip

Guard clauses keep the happy path flush-left and make failure cases obvious.

2. Pattern matching over nested ifs Depth: 4 → 2

Branches are coupled in a way that hides which conditions truly belong together. It’s difficult to see that admin is only relevant for status 200. The primary axis of decision (status code) is explicit; the secondary detail (admin) is scoped to its relevant case. Depth falls, and tests map naturally to cases.

def classify(code: Int, admin: Boolean): String = {
  if (code == 200) {
    if (admin) "ok-admin" else "ok"
  } else {
    if (code == 401) "unauthorized" else "other"
  }
}

def classify(code: Int, admin: Boolean): String = code match {
  case 200 => if (admin) "ok-admin" else "ok"
  case 401 => "unauthorized"
  case _   => "other"
}

3. Extract helpers to cap local depth Depth per function: 1–2

The happy path is clear, there’s no manual unwrapping, and indentation is capped. Combinators encode a common shape, so future readers recognize the pattern quickly.

def render(p: Product): String = {
  if (p.stock > 0) {
    if (p.price > 100) s"🔥 ${p.name}" else s"${p.name}"
  } else {
    "sold-out"
  }
}

private def hotTag(p: Product): String =
  if (p.price > 100) s"🔥 ${p.name}" else s"${p.name}"

def render(p: Product): String =
  if (p.stock <= 0) "sold-out" else hotTag(p)

Note

Depth is measured at the function level; extraction keeps each function shallow and testable.