Primitive Obsession

Symptom

Domain concepts represented as raw strings, numbers, or booleans — phone number is a string, money is a number, status is a code.

Goal

Each domain concept has a small typed home — Money, PhoneNumber, OrderId, Status — that knows its rules.

Smellier version

function priceFor(cents, currency) {
  // ...
}

Fresher version

class Money { /* amount + currency, with arithmetic */ }
function priceFor(money) {
  // ...
}

Savings

Misuse becomes a type error; behavior accretes around the concept; refactoring is local to the wrapper.

Note

Validation and formatting scatter across every consumer; the type system can't catch wrong primitives in the wrong slot.