ADR 0004: Model msgstr by Semantics Instead of Always Using Vec<String>

• Status: Accepted
• Date: 2026-03-15

Context

Most PO entries are singular.

Representing every translation set as a Vec<String> imposes avoidable overhead:

• per-item vector allocation pressure
• extra branching and resizing for the common singular case
• less direct expression of PO semantics

Decision

Represent msgstr with semantic variants:

• None
• Singular
• Plural

The owned model uses MsgStr, and the borrowed model uses BorrowedMsgStr<'a>.

Consequences

Positive:

• better fit for actual PO structure
• lower overhead for common singular items
• cleaner basis for both owned and borrowed parsing

Negative:

• API changed from a plain Vec<String> shape
• serializer and parser logic need variant-aware handling
• interoperability code may need small adjustments