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- log-writes-must-survive-rollback.good.al: fixed invalid trigger OnRun(var Rec: ...) declaration; Rec is implicit when TableNo is set. - exposed-objects-must-be-in-a-permission-set.md: distinguished the three exposure mechanisms (page/query web service or API, codeunit published as a web service, [ServiceEnabled] bound action on a page) and their actual permission targets (page/query "..." = X vs codeunit "..." = X). - code-must-not-change-workdate.md: scoped from an absolute "never" to "not as a side effect of unrelated logic" - verified real WorkDate(x) setter usage in BCApps demo-data generators and test codeunits. - bcpt-scenarios-must-be-app-specific.md: SingleInstance and StartScenario/EndScenario reframed as context-dependent patterns, not mandatory requirements - BCPT Create Customer uses neither. - test-feature-scenario-tags.good.al/.bad.al: replaced the invented LibrarySales.CreateCustomerWithPrice/"Item Price Mgt." calls with a real, verified price-list-line test using Library - Sales/Library - Inventory/ Library - Price Calculation. - page-design-must-match-bc-page-type-conventions.md: scoped the missing UsageCategory anti-pattern to pages intended as searchable entry points. - defensive-vs-offensive-code-must-match-blast-radius.md/.good.al/.bad.al: replaced the VAT registration number "low blast radius" example with a genuinely cosmetic field (customer home page URL). - source-organized-by-feature-not-object-type.md: anti-pattern reframed as inconsistency with a repo's own convention, not the object-type scheme itself. - pictures-must-use-media-not-blob.md: removed leftover "image variants" wording contradicting the already-corrected MediaSet description. Proactively fixed while sweeping all fixtures for invented APIs: - given-blocks-must-cover-full-precondition-chain.bad.al: PostSalesOrder called with wrong arity and referenced an undeclared variable. - ui-test-codeunit-naming.good.al/.bad.al: replaced the same fake "Item Price Mgt."/TestPage "Item Price" with real Library - Sales calls and the real Customer Card TestPage. Worklist completeness: added review-skill cues for the 12 of 18 new rules that had none (al-appsource-review.md, al-data-modeling-review.md, al-error-handling-review.md, al-security-review.md, al-style-review.md x3, al-testing-review.md x2, al-ui-review.md, al-upgrade-review.md, al-web-services-review.md), and fixed test-feature-scenario-tags' cue, which only matched the compliant (tagged) shape instead of the anti-pattern (untagged/generic-named test). Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
26 lines
2.8 KiB
Markdown
26 lines
2.8 KiB
Markdown
---
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bc-version: [all]
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domain: error-handling
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keywords: [defensive-programming, offensive-programming, fail-fast, blast-radius, guarded-lookup]
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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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# Match defensive vs. offensive error handling to the blast radius of being wrong
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## Description
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Whether code should guard gracefully (defensive) or fail loudly (offensive/fail-fast) is not a matter of habit or a blanket house style — it depends on what happens downstream if the guarded condition is silently defaulted or skipped. Treating every missing value the same way, defensively or offensively, is itself the anti-pattern: uniform defensiveness hides the failures that matter most, while uniform fail-fast turns ordinary, expected absence into unnecessary crashes. Two fields can look structurally identical — both read from a related record, both potentially missing — and still deserve opposite treatment depending on what they feed.
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## Best Practice
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Trace what a silently-defaulted or skipped value actually reaches before deciding how to guard it. If it reaches a posted ledger amount, a tax/VAT calculation, a quantity or price actually used in a transaction, or a legally/compliance-facing output, code offensively: let the lookup fail loud (`TestField`, an unguarded `Get()` expected to always succeed, or an explicit `Error`) so a human sees the problem before anything posts. If it is cosmetic, informational, or easily corrected after the fact (a display field, an optional UI enhancement, a report not yet run), code defensively — but the fallback must be an explicit, deliberately-chosen, named business value, never a blank or zero that is merely the datatype default. When genuinely unsure which category a field falls into, that is a question to resolve explicitly with whoever owns the requirement, not a coin flip.
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See sample: `defensive-vs-offensive-code-must-match-blast-radius.good.al`.
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## Anti Pattern
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Guarding two fields the same way purely out of habit, without analyzing what each one feeds. A low-blast-radius field, such as a customer's home page URL shown only for convenience on a printed document, and a high-blast-radius field, such as the VAT posting group that determines VAT actually applied to a posted transaction, are both wrapped in the same `if Header.Get(...) then ... else` pattern with a blank/zero fallback — leaving the posting-critical field free to post with a silently wrong value. A VAT registration number is not a safe stand-in for the low-risk side of this example: it is legally relevant, often validated, and can feed external VAT services or mandated document output, so it belongs on the offensive/fail-fast side alongside the posting group, not next to it as the "safe" contrast.
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See sample: `defensive-vs-offensive-code-must-match-blast-radius.bad.al`.
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