What variable names ARE allowed in EK9 despite the naming rules?

← Variable Naming Rules and Conventions · Ref: Q923

EK9 allows three categories of names that might seem like they would be banned:

1. SINGLE-CHARACTER NAMES: x, y, z, i, j, k, n, t — always allowed for math variables, loop counters, generic type parameters.

2. COMPOUND WORDS containing banned roots: connectionState, dataProcessor, bufferSize, inputValidator, configPath — the banned word is part of a larger descriptive name.

3. MATH/SCIENCE VARIABLES: theta, radius, alpha, delta — domain-specific short names that carry clear meaning in context.

EK9 bans exactly 12 non-descriptive names (E11031): temp, tmp, flag, flg, data, dat, object, obj, value, val, buffer, buf. These are case-insensitive. Names like str, num, item, result, input, output, count, index, list, map, set, key, status, state, type, config, param, arg, var, ret, res are NOT banned.

Separately, E11032 bans operator keywords as variable names: empty, length, contains, abs, sqrt, close, matches.

The rule is simple: bare generic names from the 12-name list are banned, but descriptive names (including compound words) are always fine.

Example

defines module qa.naming.allowedexceptions

  defines function

    <?-
      Shows math variables — single-char and short science names.
    -?>
    computeHypotenuse() as pure
      ->
        x as Float
        y as Float
      <- hypotenuse as Float: sqrt(x * x + y * y)

  defines program

    AllowedExceptionsDemo()
      stdout <- Stdout()

      // ALLOWED: single-character math variables
      x <- 3.0
      y <- 4.0
      z <- computeHypotenuse(x, y)
      stdout.println(`Hypotenuse: ${z}`)

      // ALLOWED: single-character loop counters
      i <- 1
      j <- 2
      k <- 3
      stdout.println(`Counters: ${i}, ${j}, ${k}`)

      // ALLOWED: compound words with banned roots
      connectionState <- "active"
      dataProcessor <- "xml"
      bufferSize <- 4096
      configPath <- "/etc/app.conf"
      stdout.println(`State: ${connectionState}`)
      stdout.println(`Processor: ${dataProcessor}, Size: ${bufferSize}`)
      stdout.println(`Config: ${configPath}`)

      // ALLOWED: math/science domain names
      theta <- 1.57
      radius <- 10.0
      stdout.println(`Theta: ${theta}, Radius: ${radius}`)

Common mistakes

E11031 — The bare name 'dat' is banned (E11031), but the compound word 'connectionState' is allowed because it describes what kind of state.

Incorrect:

      dat <- "active"
      dataProcessor <- "xml"
      bufferSize <- 4096
      configPath <- "/etc/app.conf"
      stdout.println(`State: ${dat}`)

Correct:

      connectionState <- "active"
      dataProcessor <- "xml"
      bufferSize <- 4096
      configPath <- "/etc/app.conf"
      stdout.println(`State: ${connectionState}`)

Keywords: compound, E11031, math, naming, allowed, exception, single-char