Data Kotlin active any

Keep custom equality and hash codes contract-safe

data-kotlin-017

Intent

Prevent collections and comparisons from breaking because equality and hashing disagree.

Applicability

Applies to Kotlin classes with custom equals or hashCode. Return unknown when only generated data-class behavior is used.

What to inspect

Custom equals, hashCode, mutable identity fields, and symmetry or null handling.

Pass criteria

equals is reflexive, symmetric, transitive, and consistent, and hashCode matches the same identity fields.

Fail criteria

Equality or hashing uses different fields, breaks symmetry across subclasses, or depends on mutable state in unsafe ways.

Do not flag

Plain data classes using compiler-generated equals and hashCode unchanged.

Confidence guidance

HIGH when custom methods clearly violate the contract. MEDIUM when hidden superclass behavior matters. LOW when only one method is visible.

Remediation

Define equality and hashing from the same stable identity and prefer data classes when appropriate.

Pass example

override fun equals(other: Any?) = other is User && id == other.id
override fun hashCode() = id.hashCode()

Fail example

override fun equals(other: Any?) = other is User && email == other.email
override fun hashCode() = id.hashCode()