bcquality/community/knowledge/performance/order-case-branches-by-frequency.md
Jesper Schulz-Wedde 9a4198eb28 Add [all] sentinel to bc-version; apply to version-agnostic knowledge
Most of the corpus — FindSet/SetLoadFields/CalcFields patterns, permission
sets, SingleInstance codeunits, DataClassification, IsolatedStorage,
transaction scope, SecretText — describes BC platform behaviour that is
identical across supported versions. The seed [26..28] range on every
file implied a version-specificity the content does not actually have,
and there was no way to express "applies to every version" in the
schema the way [w1] and [all] already do for countries and
application-area.

Extend the v1 schema with a universal sentinel for bc-version, parallel
to the sentinels already defined for the other dimensions:

  bc-version: [all]         # applies to every BC version

[all] is mutually exclusive with explicit versions. Range shorthand
([26..28]) and explicit lists ([26, 27, 28]) continue to work for files
genuinely tied to a version-gated API or deprecation.

Update read.md (field definition, matching semantics, partial-context
rule), write.md (default to [all], use ranges only with a concrete
reason), README.md (frontmatter example), and the CI validator. All
forty existing knowledge files and the three action skills convert to
[all]; none of the current content is version-gated. Validator passes.
2026-04-23 16:00:03 +02:00

1.6 KiB

bc-version domain keywords technologies countries application-area
all
performance
case
branch
frequency
control-flow
hot-path
al
w1
all

Order case branches by frequency

Seed article. Ported from BC Code Intelligence to seed the community corpus. Community contributors are invited to expand or refine.

Description

The AL case statement evaluates branches in the order they appear. When the distribution of the discriminator is heavily skewed — one or two values handle the vast majority of records, and the rest handle edge cases — the average cost of the statement is dominated by how many branches precede the common one. For evenly distributed discriminators the order does not matter; for skewed distributions it changes the hot-path cost of every call site.

Best Practice

Where the runtime frequency of values is known or measurable, list the common branches first. An else arm that handles unexpected values belongs last. When the common branch is also the simplest to evaluate, the placement compounds: the hot path is both short and cheap, and the uncommon branches are never touched on typical records.

See sample: order-case-branches-by-frequency.good.al.

Anti Pattern

Ordering branches alphabetically, by enum declaration order, or by "logical grouping" when the runtime distribution is heavily skewed. Every common record pays the cost of evaluating every uncommon branch first; on a posting routine processing thousands of rows the overhead is measurable.

See sample: order-case-branches-by-frequency.bad.al.