Reza

Class

2 min read

Warning

با class و بی کلاس مسعله این است.!

class Contact(val id: Int, var email: String)
 
fun main() {
    val contact = Contact(1, "mary@gmail.com")
    println(contact.email)
}

اگه نخواهیم از class استفاده کنیم!

If you’d like to create an object similar to Contact without using a class, you can use a data structure like a Map or data class to hold the data. Here’s how you can achieve that:

1. Using a function with a Map:

You can use a Map to represent the contact details.

fun createContact(id: Int, email: String): Map<String, Any> {
    return mapOf("id" to id, "email" to email)
}
 
fun main() {
    val contact = createContact(1, "mary@gmail.com")
    println(contact["email"]) // Output: mary@gmail.com
}

2. Using a lambda to create an object-like structure:

You can also use the apply function or a similar approach to initialize a Map in a more inline fashion.

fun main() {
    val contact = mutableMapOf<String, Any>().apply {
        put("id", 1)
        put("email", "mary@gmail.com")
    }
    println(contact["email"]) // Output: mary@gmail.com
}

These approaches avoid using a class while still providing a way to represent and store data like in the original Contact example.

Data Holder

If you want to have an output like println(contact.email) without using a class, you can create a custom data holder using a data class or a lambda with property access syntax. However, if you truly want to avoid using a class, the best approach would be to use a Map and make it behave like an object.

Here’s how you can do it:

Using Map and extension properties:

You can extend the Map with properties to allow access like a class.

fun createContact(id: Int, email: String): Map<String, Any> {
    return mapOf("id" to id, "email" to email)
}
 
val Map<String, Any>.email: String
    get() = this["email"] as String
 
fun main() {
    val contact = createContact(1, "mary@gmail.com")
    println(contact.email) // Output: mary@gmail.com
}

Explanation:

  • We use a Map<String, Any> to store the Contact data.
  • We create an extension property email for the Map, which allows us to access the value like a class property (contact.email).

This allows you to simulate the class-like behavior while avoiding the use of a formal class.

Trailing commas

کاماهای دنباله دار، کامای انتها

A trailing comma is a comma symbol after the last item in a series of elements:

class Person(
    val firstName: String,
    val lastName: String,
    val age: Int, // trailing comma
)

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