Infix functions in DSLs in Kotlin - Mini Project: Build & Apply

Using Infix Functions in Kotlin DSLs

📖 Scenario: Imagine you are creating a small Kotlin program to build a simple shopping list using a Domain Specific Language (DSL). You want to use infix functions to make the code easy to read and write, like a natural language.

🎯 Goal: Build a Kotlin program that uses infix functions to add items with quantities to a shopping list in a clear and readable way.

📋 What You'll Learn

Create a data class called Item with name and quantity properties

Create an infix function called qty to set the quantity of an item

Create a list called shoppingList to hold Item objects

Add items to the shoppingList using the infix qty function

Print the shopping list with item names and quantities

💡 Why This Matters

🌍 Real World

Infix functions help make Kotlin DSLs more readable and expressive, useful for configuration files, build scripts, and custom mini-languages.

💼 Career

Understanding infix functions and DSLs is valuable for Kotlin developers working on clean APIs, build tools like Gradle, or domain-specific applications.

1

Create the Item data class

Create a Kotlin data class called Item with two properties: name of type String and quantity of type Int.

Kotlin

# Your code here

Need a hint?

Use data class Item(val name: String, val quantity: Int) to define the class.

2

Create the infix function qty

Create an infix function called qty that extends String. It should take an Int parameter called amount and return an Item with the string as the name and amount as the quantity.

Kotlin

data class Item(val name: String, val quantity: Int)

# Your code here

Need a hint?

Define the infix function with infix fun String.qty(amount: Int): Item and return Item(this, amount).

3

Create the shoppingList and add items

Create a mutable list called shoppingList of type Item. Add these items using the infix qty function: "Apples" qty 5, "Bananas" qty 3, and "Carrots" qty 7.

Kotlin

data class Item(val name: String, val quantity: Int)

infix fun String.qty(amount: Int): Item {
    return Item(this, amount)
}

# Your code here

Need a hint?

Use mutableListOf() to create the list and add items with shoppingList.add("Apples" qty 5).

4

Print the shopping list

Use a for loop with variables item to iterate over shoppingList. Print each item's name and quantity in the format: "Apples: 5".

Kotlin

data class Item(val name: String, val quantity: Int)

infix fun String.qty(amount: Int): Item {
    return Item(this, amount)
}

val shoppingList = mutableListOf()
shoppingList.add("Apples" qty 5)
shoppingList.add("Bananas" qty 3)
shoppingList.add("Carrots" qty 7)

# Your code here

Need a hint?

Use for (item in shoppingList) and println("${item.name}: ${item.quantity}") to print each item.