rspec/rules/S2175/kotlin/rule.adoc

== Why is this an issue?

The Kotlin collections API has methods that allow developers to overcome type-safety restriction of the parameter, such as `Iterable.contains`. When the actual type of the object provided to these methods is not consistent with the target collection's actual type, those methods will always return `false` or `null`. This is most likely unintended and hides a design problem.


This rule raises an issue when the type of the argument of the following APIs is unrelated to the type used for the collection declaration:

* `MutableCollection.remove`
* `MutableCollection.removeAll`
* `MutableCollection.retainAll`
* `Array.contains`
* `Array.indexOf`
* `Array.lastIndexOf`
* `Collection.containsAll`
* `Iterable.contains`
* `Iterable.indexOf`
* `Iterable.lastIndexOf`
* `List.indexOf`
* `List.lastIndexOf`
* `Map.contains`
* `Map.containsKey`
* `Map.containsValue`
* `Map.get`
* `MutableMap.remove`



=== Noncompliant code example

[source,kotlin]
----
fun main(args: Array<String>) {
    val map: MutableMap<Int, Any> = mutableMapOf()
    map.remove<Any, Any>("42") // Noncompliant; will return 'null' for sure because 'map' is handling only Integer keys

    // ...
    val list: MutableList<String> = mutableListOf()
    val integer = Integer.valueOf(1)
    if (list.contains<Any>(integer)) { // Noncompliant; always false.
        list.remove<Any>(integer) // Noncompliant; list.add(integer) doesn't compile, so this will always return 'false'
    }
}
----

=== Compliant solution

[source,kotlin]
----
fun main(args: Array<String>) {
    val map: MutableMap<Int, Any> = mutableMapOf()
    map.remove(42)

    // ...
    val list: MutableList<String> = mutableListOf()
    val str = ""
    if (list.contains(str)) {
        list.remove(str)
    }
}
----