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Contributed by CURABIS ApS, generalized from patterns observed across real AppSource/PTE development. Each article follows the knowledge file format (frontmatter, Description/Best Practice/Anti Pattern, sibling .good.al/.bad.al samples).
28 lines
1.4 KiB
Markdown
28 lines
1.4 KiB
Markdown
---
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bc-version: [all]
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domain: style
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keywords: [var-parameter, by-reference, pass-by-reference, literal, constant, compile-error, procedure-call]
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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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# A `var` parameter must be called with a variable, never a literal or expression
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> Contributions welcome — open a PR to refine or extend this article.
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## Description
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When a procedure declares a parameter with `var`, that parameter is passed by reference: the callee writes back into the caller's own memory location. This means the argument at the call site must be an actual variable, something with an address. A string literal, a numeric constant, or a computed expression has no address to write back to, so passing one to a `var` parameter fails to compile. Before writing a call, check the callee's signature for `var` on each parameter position being supplied a literal or expression — if present, a variable declared in the caller's own scope must be used instead.
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## Best Practice
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Declare a variable in the caller's scope and pass it to the `var` parameter.
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See sample: `var-parameters-require-an-addressable-variable.good.al`.
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## Anti Pattern
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Passing a literal or a computed expression to a `var` parameter position fails to compile, because neither has an address the callee can write back to.
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See sample: `var-parameters-require-an-addressable-variable.bad.al`.
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