creating a random list of coins from a repository-CodePudding

I'm trying to build a simple app that would display a coin collection for each user I type into a textfield. The coin collection would have to be unique to each user. I already have the repository for the coins. How do I generate a new random coin collection for each user? Each collection could have multiple coins of the same value but with different years.

object CoinRepository {

fun getCoinCollection(): List<Coin> {
    return listOf(
        Coin(
            id = 1,
            name = "Penny",
            year = (1900..2022).random()
        ),
        Coin(
            id = 2,
            name = "Nickel",
            year = (1900..2022).random()
        ),
        Coin(
            id = 3,
            name = "Dime",
            year = (1900..2022).random()
        ),
        Coin(
            id = 4,
            name = "Quarter",
            year = (1900..2022).random()
        ),
        Coin(
            id = 5,
            name = "Dollar",
            year = (1900..2022).random()
        )
    )
}

}

data class Coin(
val id: Int,
val name: String,
val year: Int

)

CodePudding user response：

You could do something like this:

import kotlin.random.Random

// Define your specific data in an enum, with all the relevant properties
enum class Denomination(val id: Int, val label: String) {
    PENNY(1, "Penny"),
    NICKEL(2, "Nickel"),
    DIME(3, "Dime"),
    QUARTER(4, "Quarter"),
    DOLLAR(5, "Dollar");
    
    companion object {
        // a simple way to return one of the instances at random - the property
        // avoids creating a new values() array every time it's called
        val values = values()
        fun random() = values.random()
    }
}

// a basic way to keep the random date logic in the Coin class itself, using
// a default parameter. No validation involved obviously!
data class Coin(val id: Int, val label: String, val year: Int = (1900..2022).random())

// get a random number of Coins, within a certain min/max
fun getCoinCollection() = List(Random.nextInt(1, 10)) {
    // pulls a random coin type and creates a Coin, letting its constructor
    // handle the random date (you could do it here if you want)
    Denomination.random().run { Coin(id, label) }
}

There's more than one way to organise it, I've thrown a few things in there so you can get some ideas of how you might do it. But it's basically a function that creates a list of random length (within limits), and then creates a Coin for each item, using a random Denomination

The Denomination enum is just a way to define your data, a fixed set of possible items with certain properties. Because enums generate that values() array automatically (containing all its instances) you can easily pick one at random. You could also extend the properties here to include a valid date range for each coin type, etc

You could just automatically generate the label and id values from the enum's name and ordinal properties (e.g. "PENNY" and 0) so you don't need to declare them explicitly - I feel like it's usually a good idea to decouple the data from how it's represented in the enum in code, but that's your call - I've included it so you can see how