diff --git a/custom/knowledge/style/variable-names-must-be-semantically-descriptive.md b/custom/knowledge/style/variable-names-must-be-semantically-descriptive.md new file mode 100644 index 0000000..397164d --- /dev/null +++ b/custom/knowledge/style/variable-names-must-be-semantically-descriptive.md @@ -0,0 +1,65 @@ +--- +bc-version: [all] +domain: style +keywords: [variable-naming, semantic-naming, readability, magic-name, self-documenting] +technologies: [al] +countries: [w1] +application-area: [all] +--- + +# Variable names must describe what the value means, not just its type + +## Description + +A variable name must let a reader understand what the value represents +without having to trace every place it is assigned or used. A name built +from a generic type abbreviation plus a sequence number or letter — +`Amt1`, `Amt2`, `Var1`, `OptA`, `Int3`, `TempX` — fails this test: it tells +the reader the data type, which AL already shows via the declaration, but +nothing about the business meaning. `AmountInclVAT` is immediately +readable; `Amt1` requires the reader to go find out what Amt1 is actually +used for. + +The fix is not "add more letters" — it is to name the variable for the +business concept it holds: `AmountInclVAT`, `CustomerDiscountPct`, +`RemainingQuantity`, `IsOverdue`. If two variables genuinely hold the same +kind of value in a comparison or calculation (e.g. two amounts being +subtracted), name them for their distinct roles in that calculation +(`OriginalAmount` / `AdjustedAmount`), not for their shared type +(`Amt1` / `Amt2`). + +**Exception:** short-lived loop counters and array indices (`i`, `idx`, +`x`) are an accepted convention precisely because their entire meaning is +visible in the two or three lines of the loop that declares and uses them. +This exception does not extend to variables that live longer than a tight +loop body or that carry business meaning beyond "the current position." + +## Best Practice + +```al +var + AmountInclVAT: Decimal; + RemainingQuantity: Decimal; + IsOverdue: Boolean; +... +for idx := 1 to ArrayLen(SalesLine) do + TotalAmount += SalesLine[idx]; +``` + +## Anti Pattern + +```al +var + Amt1: Decimal; + Amt2: Decimal; + OptA: Option; + TempX: Integer; +... +if OptA = 1 then + Amt1 := Amt2 - TempX; +``` + +A reviewer reading `Amt1 := Amt2 - TempX;` cannot tell what this line is +computing without opening the variable declarations and searching for every +other assignment to `Amt2` and `TempX` first. The same line as +`AmountInclVAT := AmountExclVAT - DiscountAmount;` needs no further lookup.