mirror of
https://github.com/microsoft/BCQuality.git
synced 2026-08-06 17:36:53 +01:00
5706959e4a
* Fix lifecycle compatibility guidance Correct high-confidence Business Central guidance and samples for upgrade tags, collectible errors, trigger semantics, obsoletion, events, interfaces, API contracts, and test transactions. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: e05a43e7-6448-4d67-9c73-798523f5d945 * Address guidance review findings Gate SecretText guidance to BC23 and clarify that the collectible-error sample intentionally emits a message-only blocking aggregate. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: e05a43e7-6448-4d67-9c73-798523f5d945 --------- Co-authored-by: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com>
26 lines
2.2 KiB
Markdown
26 lines
2.2 KiB
Markdown
---
|
|
bc-version: [16..]
|
|
domain: interfaces
|
|
keywords: [interface, defaultimplementation, enum-implements-interface, fallback, extensible-enum, implementation-property]
|
|
technologies: [al]
|
|
countries: [w1]
|
|
application-area: [all]
|
|
---
|
|
|
|
# Set DefaultImplementation on an enum so an unmapped value still resolves to an interface
|
|
|
|
## Description
|
|
|
|
An `enum` that `implements` an interface maps each value to a codeunit through the `Implementation` property. But an extensible enum can carry values that set no `Implementation` — values added later by an extension, or a value left intentionally blank. Assigning such a value to an interface variable and calling a method on it fails at runtime unless the enum provides a fallback. The enum-level `DefaultImplementation` property names the codeunit used whenever a value has no explicit `Implementation`, so resolution always yields a usable object. LLMs are generally unaware this property exists and leave the gap open.
|
|
|
|
## Best Practice
|
|
|
|
On any extensible enum that implements an interface, set `DefaultImplementation = <Interface> = <Codeunit>;` at the enum level, pointing at a safe implementation that does nothing harmful. Values with their own `Implementation` keep using it; declared values without one resolve to the default. For an ordinal that matches no currently declared value — for example persisted data left after an enum extension is uninstalled — runtime 7.0 and later can use `UnknownValueImplementation` as a distinct fallback. Do not recommend that property to apps targeting an earlier runtime.
|
|
|
|
See sample: `set-defaultimplementation-on-enum.good.al`.
|
|
|
|
## Anti Pattern
|
|
|
|
An extensible `enum ... implements <Interface>` where at least one value sets no `Implementation` and the enum declares no `DefaultImplementation`. Code that assigns that value to an interface variable and invokes a method throws at the call site, and because the enum is extensible the failing value can be introduced by a third party long after the consumer ships. Detection signal: an enum that implements an interface, has a `value(...)` with no `Implementation`, and no enum-level `DefaultImplementation`. Add a `DefaultImplementation` mapping to close the gap.
|
|
|
|
See sample: `set-defaultimplementation-on-enum.bad.al`.
|