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Non_exhaustive attribute

As explained in Learn Rust in a Month of Lunches

The non_exhaustive attribute marks a Rust type as potentially gaining additional fields or enum variants in future versions.

The `#[non_exhaustive]` attribute marks a Rust type as open to additional fields or enum variants in future versions. It is used mostly with enums, which remain usable while requiring outside match expressions to include a final fallback check. section 13.1.5

Matching a future-proof enum

When matching an externally defined `#[non_exhaustive]` enum, handle the known variants and then add a final fallback case. That fallback protects the match if a later version adds another variant. section 13.1.5

How Learn Rust in a Month of Lunches covers it

How deep it goes
Defines the attribute and explains its effect on enum matching, but does not detail compiler internals or field-specific behavior.
Examples
Uses externally defined non-exhaustive enums and the required final fallback match case as the practical example.
What it assumes
Assumes familiarity with Rust attributes and enum matching, while explaining the need for a final fallback check.
What you can do after
Apply it to future-proof Rust types and write matches that tolerate newly added enum variants.
How it connects
Connects Rust attributes with enums, enum variants, and pattern matching.
Cover of Learn Rust in a Month of Lunches
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Related concepts

This explainer was generated by Manning's knowledge graph from the text of Learn Rust in a Month of Lunches. The section links point to the parts of the book it draws on.