Avoid Empty Wrapper Types
RUST-AVOID-EMPTY-WRAPPER-TYPES
Summary
Add a wrapper type only when it carries an invariant, behavior, or ownership boundary. Otherwise it adds conversions and concepts without improving correctness.
Rule
Avoid wrapper types that add no invariant, behavior, or ownership clarity.
Why
A wrapper type should earn its name by adding an invariant, behavior, ownership boundary, or API meaning. A tuple struct or newtype that only renames an existing value adds conversion cost and another concept without helping the reader.
Helps
Helps keep the type system meaningful by reserving new names for real invariants, ownership boundaries, validation rules, or domain concepts.
Limits
Use a wrapper when it prevents unit confusion, restricts construction, hides representation, implements a trait coherently, or marks a boundary that callers need to see.
Agent Instruction
Avoid wrapper types that add no invariant, behavior, or ownership clarity; a wrapper should earn its
name.Mechanisms
Look for validation constructors, private fields, trait implementations, serialization policy, or ownership changes. If none exist, prefer the underlying type or a type alias.