Equals Always Returns

ID

kotlin.equals_always_returns

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Kotlin

Tags

correctness, equals

Description

Reports equals() implementations whose body always returns a constant true or false.

An equals() that unconditionally returns a constant violates the Any.equals contract and makes collection membership, deduplication, and comparisons unreliable for instances of the class.

Rationale

// Bad — always equal, any two instances compare as equal
override fun equals(other: Any?) = true  // FLAW

// Bad — never equal, objects are never found in sets or maps
override fun equals(other: Any?): Boolean {
    return false  // FLAW
}

// Good — real structural comparison
override fun equals(other: Any?): Boolean {
    if (this === other) return true
    if (other !is Widget) return false
    return id == other.id
}

Remediation

Implement structural equality by comparing the meaningful fields of the class. Always override hashCode() consistently: objects that are equals must have the same hashCode.

References