CODEWITHSUNDEEP
kotlin
BobHy
BobHy

Reputation: 1734

How to declare map with types of user type properties

I have a custom type declared as:

data class User (
    val name: String,
    val rank: Int
)

and wish to declare a Map whose keys are the name and values are the ranks, referring to the types as declared for User.

I have tried kotlin reflection,

val foo1 = Map <User::name, User::rank>()   //compiler error 'not enough information to infer type...'

Is there a normative way to do this?

So far, I "just have to know" the types for key and value, e.g:

val foo = Map <String, Int>()

But this is brittle, and would break if I change User in the future, e.g .rank from Int to Float. Of course, I wouldn't remain ignorant of my oversight for long, I expect the compiler would start complaining, but is there something elegant I can do now?

Upvotes: 0

Views: 266

Answers (1)

aSemy
aSemy

Reputation: 7109

You could use a value class to define the user's name and rank.

@JvmInline
value class UserName(val name: String)

@JvmInline
value class UserRank(val rank: Int)

data class User (
    val name: UserName,
    val rank: UserRank,
)

val userMap = Map<UserName, UserRank>() // type-safe map

Or create a value class that implements Map<String, Int>, and use delegation.

@JvmInline
value class UserMap(
  private val map: Map<String, Int>
) : Map<String, Int> by map {

  operator fun contains(user: User): Boolean = 
    map[user.name] == user.rank
}

Or both together!

Upvotes: 1

Related Questions