Kotlin Fundamentals Skill

Quick Start

// Variables
val immutable = "constant"
var mutable = "variable"

// Functions
fun greet(name: String): String = "Hello, $name"

// Classes
data class User(val id: Int, val name: String)

// Null safety
val user: User? = null
user?.name // safe call
user?.name ?: "Unknown" // elvis operator

Key Concepts

Null Safety

• ? for nullable types
• !! for non-null assertion (avoid)
• ?: elvis operator for defaults
• ?.let { } for null-safe blocks

Extension Functions

fun String.isValidEmail(): Boolean = contains("@")
val valid = "user@example.com".isValidEmail()

Scope Functions

• apply: Configure object
• let: Transform
• run: Execute with context
• with: Receiver operations
• also: Side effects

Coroutines

viewModelScope.launch {
    val data = withContext(Dispatchers.IO) {
        fetchData()
    }
}

SOLID Principles Summary

1. SRP: One responsibility per class
2. OCP: Open for extension, closed for modification
3. LSP: Substitutable subtypes
4. ISP: Specific interfaces
5. DIP: Depend on abstractions

Learning Resources

• Kotlin Docs
• Kotlin Coroutines
• Effective Kotlin