Kotlin: How to check if enum contains a given String without messing with Exceptions? - kotlin

Question

Why there is no contains method in enum classes (as well as in Java)? And how to implement it elegantly? Now I'm using this ugly approach:
val contains: Boolean =
try {
MyEnum.valueOf("some string")
true
} catch (e: IllegalArgumentException) {
false
}

Answer 1

enumContains
You can create an enumContains function similar to Hound Dog's answer but using reified type parameters instead.
You cannot create a JVM independent solution in Kotlin 1.0 but you can in Kotlin 1.1 using enumValues.
Kotlin 1.1
/**
* Returns `true` if enum T contains an entry with the specified name.
*/
inline fun <reified T : Enum<T>> enumContains(name: String): Boolean {
return enumValues<T>().any { it.name == name}
}
Kotlin 1.0
/**
* Returns `true` if enum T contains an entry with the specified name.
*/
inline fun <reified T : Enum<T>> enumContains(name: String): Boolean {
return T::class.java.enumConstants.any { it.name == name}
}
Usage
enumContains<MyEnum>("some string") // returns true or false
enumValueOfOrNull
If you also need the actual enum entry then you might consider creating an enumValueOfOrNull function instead.
Kotlin 1.1
/**
* Returns an enum entry with the specified name or `null` if no such entry was found.
*/
inline fun <reified T : Enum<T>> enumValueOfOrNull(name: String): T? {
return enumValues<T>().find { it.name == name }
}
Kotlin 1.0
/**
* Returns an enum entry with the specified name or `null` if no such entry was found.
*/
inline fun <reified T : Enum<T>> enumValueOfOrNull(name: String): T? {
return T::class.java.enumConstants.find { it.name == name }
}
Usage
enumValueOfOrNull<MyEnum>("some string")

Answer 2

You can just take values Array of your enum and use contains over it. For example:
Planets.values().map { it.name }.contains("EARTH")
But for this you need to have correct string value so you might uppercase it before search.
If you want to find enum by its value take a look at the Reverse Lookup for enums.
Edit:
As #JamesBassett suggested you can optimize it to stop looking once it finds a match.
Planets.values().any { it.name == "EARTH" }

Answer 3

You could do something like this:
fun <T : Enum<*>> KClass<T>.contains(value: String): Boolean {
return this.java.enumConstants.any { it.name == value }
}
MyEnum::class.contains("some string")

Answer 4

or if you are really adventurous
enum MyEnum {
MY_1, MY_2;
companion object {
fun isInEnum(someString: String) {
return try {
valueOf(someString)
true
} catch (e: Exception) {
false
}
}
}
}