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The article was rewritten to say a reset is required only when the value can carry over, and its H1 was updated to match, but three artefacts still carried the old "always initialize to false" premise: - The slug still read `initialize-ishandled-to-false-before-publishing`, which contradicts the body. The slug is not cosmetic: Build-KnowledgeIndex.ps1 ranks candidates on keywords, frontmatter dimensions, domain, path and title, so a stale path pushes selection back toward the behaviour this change narrows. Renamed to `reset-ishandled-only-when-the-value-can-carry-over`, following the existing precedent for conditional slugs such as `unreleased-symbol-change-is-not-a-breaking-change`. - Keywords still listed `initialization` and `deterministic` and omitted `false-positive`, the tag this repository uses for suppression articles. Replaced with `carry-over` and `loop-iteration` and added `false-positive`. - The good sample demonstrated only the "prefer separate fresh locals" clause and contained no reset at all, so the article's headline case had no positive example. It was also asymmetric with the bad sample, which gained a loop procedure showing a local that carries `true` into the next iteration. Added the matching loop procedure to the good sample: a local declared outside the loop is reset at the top of each iteration. That case cannot be solved by introducing another local, because AL has no block scope, so it is the only shape that demonstrates the reset the article still requires. It also gives the engine the correct `suggested-code` shape for the loop finding; without it the one-click fix adapted from the good sample would propose splitting the variable rather than adding one line. Also renamed the sample codeunits from "IsHandled Init ..." to "IsHandled Carry Over ...", and updated the two references to the old slug: the events leaf skill cue and the events pin in evaluation/review-fixtures.json. validate_frontmatter.py reports 0 errors; Test-ReviewFixtures.ps1 passes with 32 cases across 16 leaf domains and resolves the events fixture to the renamed article.
26 lines
2.3 KiB
Markdown
26 lines
2.3 KiB
Markdown
---
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bc-version: [all]
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domain: events
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keywords: [ishandled, carry-over, loop-iteration, onbefore, reset, integration-event, control-flow, false-positive]
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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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# Reset IsHandled before publishing only when its value can carry over
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## Description
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A routine that raises an `OnBefore…` integration event with a `var IsHandled: Boolean` parameter passes that variable by reference, so a pre-existing `true` can affect the following control flow. AL [automatically initializes Boolean variables to `false`](https://learn.microsoft.com/en-us/dynamics365/business-central/dev-itpro/developer/devenv-al-variables#initialization), so a freshly declared local Boolean passed to one event exactly once per procedure invocation is already deterministic. Initialization does not repeat for each loop iteration: a local declared outside a loop can carry `true` from one iteration to the next even when the source contains only one textual event raise. Outside a loop, reaching a later raise after `if IsHandled then exit;` also proves the value is `false`, provided that early exit is semantically correct and does not skip required downstream events.
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## Best Practice
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Reset `IsHandled := false;` before a raise only when the value might otherwise carry over as `true`: the same variable is reused after an earlier raise without a control-flow proof that it is false, a raise is re-entered by a loop, the value comes from an input parameter, field, or global, or earlier code seeds it. Prefer separate fresh locals when independent event seams need independent handled state. A reset on a guaranteed-false fresh local used by one non-looping raise, or before a later raise reached only after a semantically valid `if IsHandled then exit;`, can be retained for readability, but its absence is not a correctness finding.
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See sample: `reset-ishandled-only-when-the-value-can-carry-over.good.al`.
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## Anti Pattern
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Raising `OnBeforeX(…, IsHandled)` when the variable can still be `true` from an earlier raise, an earlier loop iteration, or another source, so the publisher call starts with stale state. Do not match a single non-looping raise using a fresh local Boolean, or a later raise reached only after a semantically valid `if IsHandled then exit;` proves the value is false.
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See sample: `reset-ishandled-only-when-the-value-can-carry-over.bad.al`.
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