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Rust’s types make “parse, don’t validate” invariants explicit

eli.thegreenplace.net 8 min read Editor score 6/10

The piece applies the pattern to Rust, using `Option` and configuration-directory examples to show how APIs can represent whether a value meets an invariant. It’s useful guidance for designing safer interfaces and making invalid states harder to pass around.

What

“Parse, don't validate” applied to Rust encodes invariants in types rather than relying on checks and comments.

How

A `Vec` can remain empty after runtime validation, while `NonEmpty<T>` guarantees a head and makes `first()` return `&T`.

Why it matters

Encoding invariants in API types avoids repeated empty-case handling and makes assumptions visible to callers and the type system.

Read on eli.thegreenplace.net → Lobsters · 6 comments

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