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80 lines
2.8 KiB
Markdown
80 lines
2.8 KiB
Markdown
---
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bc-version: [all]
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domain: style
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keywords: [variable-naming, semantic-naming, readability, magic-name, self-documenting]
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technologies: [al]
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countries: [w1]
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application-area: [all]
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---
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# Variable names must describe what the value means, not just its type
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## Description
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A variable name must let a reader understand what the value represents
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without having to trace every place it is assigned or used. A name built
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from a generic type abbreviation plus a sequence number or letter —
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`Amt1`, `Amt2`, `Var1`, `OptA`, `Int3`, `TempX` — fails this test: it tells
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the reader the data type, which AL already shows via the declaration, but
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nothing about the business meaning. `AmountInclVAT` is immediately
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readable; `Amt1` requires the reader to go find out what Amt1 is actually
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used for.
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The fix is not "add more letters" — it is to name the variable for the
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business concept it holds: `AmountInclVAT`, `CustomerDiscountPct`,
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`RemainingQuantity`, `IsOverdue`. If two variables genuinely hold the same
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kind of value in a comparison or calculation (e.g. two amounts being
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subtracted), name them for their distinct roles in that calculation
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(`OriginalAmount` / `AdjustedAmount`), not for their shared type
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(`Amt1` / `Amt2`).
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**Exception:** short-lived variables in a handful of idiomatic, universally
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recognized roles are accepted single-letter, because their entire meaning
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is visible in the few lines that declare and use them:
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- Loop counters and array indices (`i`, `idx`, `x`).
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- The progress step counter in a `Dialog`/progress-window idiom — a status
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iterator whose only job is tracking how far a long-running process has
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gotten (`s`), and the count fed into the update call itself, e.g.
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`Window.Update(1, c)` (`c`).
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This exception does not extend to variables that live longer than that
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tight idiomatic scope, or that carry business meaning beyond "the current
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position" or "the current progress count" — a `Status` field on a table, or
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a `Counter` that is read elsewhere in the object, still needs a real name.
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## Best Practice
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```al
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var
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AmountInclVAT: Decimal;
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RemainingQuantity: Decimal;
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IsOverdue: Boolean;
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...
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for idx := 1 to ArrayLen(SalesLine) do
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TotalAmount += SalesLine[idx];
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...
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Window.Open('Processing #1#########');
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for s := 1 to Item.Count do begin
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c += 1;
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Window.Update(1, Round(c / Item.Count * 10000, 1));
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end;
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Window.Close();
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```
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## Anti Pattern
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```al
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var
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Amt1: Decimal;
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Amt2: Decimal;
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OptA: Option;
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TempX: Integer;
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...
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if OptA = 1 then
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Amt1 := Amt2 - TempX;
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```
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A reviewer reading `Amt1 := Amt2 - TempX;` cannot tell what this line is
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computing without opening the variable declarations and searching for every
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other assignment to `Amt2` and `TempX` first. The same line as
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`AmountInclVAT := AmountExclVAT - DiscountAmount;` needs no further lookup.
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