Equals Incompatible Types
ID |
kotlin.equals_incompatible_types |
Severity |
low |
Remediation Complexity |
trivial |
Remediation Risk |
low |
Remediation Effort |
low |
Resource |
Reliability |
Language |
Kotlin |
Tags |
reliability, suspicious-comparison |
Description
Reports a.equals(b) calls where the static types of a and b belong to
unrelated value-type families (for example String and Int, or Double
and Boolean). The call cannot succeed: the JDK equals implementation of
any boxed value type starts with if (other !is ThisType) return false.
Rationale
val s: String = "hello"
val n: Int = 1
s.equals(n) // FLAW — always false
"x".equals(42) // FLAW — always falseSuch a call is almost always the result of a typo or a copy-paste error.
Worse, the compiler accepts it silently because equals takes Any?, so the
bug surfaces at runtime as a feature that "never matches" — a class of bug
that is notoriously hard to reproduce from logs alone.
Remediation
If the comparison is intentional, fix the types so they actually belong to
the same family — for example by parsing the string into an Int first:
val s: String = "hello"
val n: Int = 1
n.equals(s.toIntOrNull()) // OK — both Int? after conversionIf you wrote the wrong identifier, replace it with the right one.