How does EK9 detect confusingly similar variable names?

← Code Quality · Ref: Q764

EK9 checks for variables in the same scope whose names differ by only 1-2 characters (Levenshtein distance). When detected, E11030 triggers.

WHAT IT DETECTS

Two variables like 'count' and 'coumt' differ by one character — a typo waiting to happen. Similarly 'index' and 'indx' or 'total' and 'totl'. When a developer (or AI) references the wrong one, the bug is subtle and hard to spot.

WHAT IS ALLOWED

- Names differing by 3+ characters are fine
- Prefixed/suffixed variants are fine: 'name' and 'firstName'
- Single-letter names in loop context: 'i', 'x', 'y'
- Different scopes: same-name variables in different functions

THIS EXAMPLE

The function below uses 'totalCount' and 'itemCount' — these differ by enough characters (Levenshtein distance > 2) to be clearly distinguishable. Using 'totalCount' and 'totalCoumt' would trigger E11030.

WHY THIS MATTERS

- AI assistants generate code at speed — similar names cause subtle bugs
- Code review misses single-character differences
- Autocomplete in editors may pick the wrong variable
- Debugging similar-name bugs wastes significant time

See Q290 for banned names. See Q292 for naming conventions. See Q310 for quality overview.

Example

defines module qa.codequality.similarnames

  defines function

    <?-
      This function uses clearly distinct variable names.
      'totalCount' and 'itemCount' differ by enough characters
      to be clearly distinguishable (Levenshtein distance > 2).
      Using 'totalCount' and 'totalCoumt' would trigger E11030.
    -?>
    calculateTotals()
      ->
        items as List of Integer
      <-
        result as String: "empty"

      totalCount <- 0
      itemCount <- 0
      grandTotal <- 0

      for item in items
        itemCount++
        totalCount++
        grandTotal += item

      result: `Items: ${itemCount}, Count: ${totalCount}, Total: ${grandTotal}`

  defines program

    SimilarNamesBoundaryDemo()
      stdout <- Stdout()
      numbers <- [10, 20, 30, 40, 50]
      stdout.println(calculateTotals(numbers))

Common mistakes

E11030 — Renaming 'itemCount' to 'totalCont' makes it confusingly similar to 'totalCount' (Levenshtein distance 2). Both are used in the same scope, creating risk of referencing the wrong one. Use clearly distinct names. See ek9 -h E11030 for details.

Incorrect:

      totalCount <- 0
      totalCont <- 0
      grandTotal <- 0

      for item in items
        totalCont++
        totalCount++
        grandTotal += item

      result: `Items: ${$totalCont}, Count: ${$totalCount}, Total: ${$grandTotal}`

Correct:

      totalCount <- 0
      itemCount <- 0
      grandTotal <- 0

      for item in items
        itemCount++
        totalCount++
        grandTotal += item

      result: `Items: ${itemCount}, Count: ${totalCount}, Total: ${grandTotal}`

Coming from another language?

Java: no similar-name detection. C#: no similar-name detection. Python: no similar-name detection. Go: no similar-name detection. Rust: no similar-name detection. All languages rely on code review to catch confusingly similar names. EK9: similar names (Levenshtein ≤ 2) are a compiler error.

Keywords: confusing, naming, Levenshtein, distance, E11030, quality, typo, similar, variable, names