Primitive obsession

What it means

Primitive obsession appears when strings, numbers, or booleans carry rules that belong to a domain concept. A dedicated type can validate invariants, name intent, and prevent accidental mixing. The improvement is not to wrap every value, but to give important concepts a clear home.

Example

A function accepts two strings for currency and account identifier. A money type and an account identifier type can make units and validation visible at the call site.

Limitations

Value objects add code and may complicate serialization or interoperability. A primitive is often sufficient for a local, unambiguous value. Consider repeated validation, unit confusion, and change frequency.

How to use the signal

Introduce a domain type when it protects units or invariants that recur, not when a local primitive is already unambiguous.

Weave can help compare domain-type refactors with review and rework signals. Keep type design with the owning team and use Weave to observe whether the change reduced recurring friction.