CODEWITHSUNDEEP
kotlin
user12595983
user12595983

Reputation: 147

Kotlin: Function declaration must have a name

Aim of the code: Class Pair can print out Product name and quantity, Product name stored in Class Product

class Pair<T, U>(var product: Product, var quantity: Int) {
    for ( (product,quantity) in productAndQuantityList) {
        println("Name: ${product.productName}")
        println("Quantity: $quantity")
    }
}

Above Error:(2, 9) Kotlin: Expecting member declaration Error:(2, 57) Kotlin: Function declaration must have a name

class ShoppingCart{
    private val productAndQuantityList = mutableListOf<Pair<Product,Int> >()
...
}

open class Product(
    val productName: String,
    var basePrice: Double,
    open val salesPrice: Double,
    val description: String) {
...}
  1. may i know how to change my code?
  2. after class Pair was suggested by Compiler, but should i fill in anything?
  3. Which topic should i work for, to avoid the same errors again?

Thanks!

Upvotes: 3

Views: 5761

Answers (2)

user
user

Reputation: 7604

If you want to run the for loop when the object is instantiated, then you should use an initializer. You can't simply put statements inside class definitions directly.

class Pair<T, U>(var product: Product, var quantity: Int) {
  init {
    for ( (product,quantity) in productAndQuantityList) {
        println("Name: ${product.productName}")
        println("Quantity: $quantity")
    }
  }
}

However, this code is wrong because Pair does not have access to productAndQuantityList, although ShoppingCart does. As Mathias Henze suggested, you should make a function in ShoppingCart and move the for loop into that, like this:

fun printProducts() {
  for ( (product,quantity) in productAndQuantityList) {
    println("Name: ${product.productName}")
    println("Quantity: $quantity")
  }
}

As for your Pair class, the type parameters T and U are unnecessary, as you don't use them anywhere, and the class itself is provided by the standard library (The header looks something like data class Pair<out A, out B>(val first: A, val second: B).

If you're determined to use your own Pair class, be sure to make it a data class, so it can be destructured, and change the type of productAndQuantityList to mutableListOf<Pair> (without the type parameters Pair<Product, Int>).

Update

Please read the answer by Mathias Henze, which is correct. My answer, was originally completely wrong, but I have now corrected it.

Upvotes: 5

Mathias Henze
Mathias Henze

Reputation: 2360

The productAndQuantityList is just for storing the data. The Pair class is a provided class by Kotlin. You don't need to add anything to it in your usecase.

The ability to print the product and the quantity should be a function of the ShoppingCart, so just have:

class ShoppingCart{
    private val productAndQuantityList = mutableListOf<Pair<Product,Int> >()
    // ...
    fun printContents() {
        for ( (product,quantity) in productAndQuantityList) {
            println("Name: ${product.productName}")
            println("Quantity: $quantity")
        }            
    }
}

Upvotes: 2

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