Module collation 

Collation callback trait, built-in collations, and registry (§9.4, §13.6).

Collations are pure comparators used by ORDER BY, GROUP BY, DISTINCT, and index traversal. They are open extension points.

compare is intentionally CPU-only and does not accept &Cx.

The CollationRegistry maps case-insensitive names to collation implementations and is pre-populated with the three built-in collations.

Contract

Implementations must be:

• Deterministic: same inputs always produce the same output.
• Antisymmetric: compare(a, b) is the reverse of compare(b, a).
• Transitive: if a < b and b < c, then a < c.

Structs

BinaryCollation

BINARY collation: raw memcmp byte comparison.

CollationAnnotation

An operand’s collation annotation: the collation name and where it came from.

CollationRegistry

Registry for collation functions, keyed by case-insensitive name.

NoCaseCollation

NOCASE collation: ASCII case-insensitive comparison.

RtrimCollation

RTRIM collation: trailing-space-insensitive comparison.

Enums

CollationSource

Source of a collation for precedence resolution (§13.6).

Traits

CollationFunction

A collation comparator.

Functions

resolve_collation

Resolve which collation to use for a binary comparison (§13.6).