Kotlin Standard Library

Standard Library Categories

listOf(1, 2, 3).map { it * 2 }

"hello".capitalize()
"a,b,c".split(",")

person.apply {
    name = "Alice"
    age = 25
}

1..10
kotlin.math.max(5, 10)

🔹 Collection Operations

Powerful functions for working with collections:

fun main() {
    val fruits = listOf("apple", "banana", "cherry", "date", "elderberry")
    
    // Transform collections
    val uppercased = fruits.map { it.uppercase() }
    println("Uppercase: $uppercased")
    
    // Filter collections
    val longNames = fruits.filter { it.length > 5 }
    println("Long names: $longNames")
    
    // Find elements
    val firstLong = fruits.find { it.length > 5 }
    println("First long name: $firstLong")
    
    // Group elements
    val grouped = fruits.groupBy { it.first() }
    println("Grouped by first letter: $grouped")
    
    // Aggregate operations
    val totalLength = fruits.sumOf { it.length }
    println("Total length: $totalLength")
    
    // Check conditions
    val allLowercase = fruits.all { it == it.lowercase() }
    println("All lowercase: $allLowercase")
}

🔹 String Operations

Built-in string manipulation functions:

fun main() {
    val text = "  Hello, Kotlin World!  "
    
    // Basic operations
    println("Original: '$text'")
    println("Trimmed: '${text.trim()}'")
    println("Uppercase: '${text.uppercase()}'")
    println("Lowercase: '${text.lowercase()}'")
    
    // String checks
    println("Contains 'Kotlin': ${text.contains("Kotlin")}")
    println("Starts with 'Hello': ${text.trim().startsWith("Hello")}")
    println("Ends with '!': ${text.trim().endsWith("!")}")
    
    // String manipulation
    val replaced = text.replace("World", "Universe")
    println("Replaced: '$replaced'")
    
    val parts = "apple,banana,cherry".split(",")
    println("Split result: $parts")
    
    val joined = parts.joinToString(" | ")
    println("Joined: $joined")
    
    // String templates and formatting
    val name = "Alice"
    val age = 25
    println("Formatted: ${name.padEnd(10)} is $age years old")
}

🔹 Scope Functions

Functions that execute code blocks in the context of an object:

data class Person(var name: String = "", var age: Int = 0, var city: String = "")

fun main() {
    // let - transform object and return result
    val nameLength = Person("Alice", 25).let { person ->
        println("Processing ${person.name}")
        person.name.length  // Return value
    }
    println("Name length: $nameLength")
    
    // apply - configure object and return the object
    val person = Person().apply {
        name = "Bob"
        age = 30
        city = "New York"
    }
    println("Person: $person")
    
    // also - perform side effects and return the object
    val numbers = mutableListOf(1, 2, 3).also { list ->
        println("Original list: $list")
        list.add(4)
    }
    println("Modified list: $numbers")
    
    // run - execute code block and return result
    val result = run {
        val a = 10
        val b = 20
        a + b  // Return value
    }
    println("Result: $result")
    
    // with - operate on object without extension
    val message = with(person) {
        "Hello, my name is $name, I'm $age years old and live in $city"
    }
    println(message)
}

🔹 Ranges and Progressions

Work with ranges of values efficiently:

fun main() {
    // Basic ranges
    val range1 = 1..10
    val range2 = 1 until 10  // Excludes 10
    val range3 = 10 downTo 1
    
    println("1..10 contains 5: ${5 in range1}")
    println("1 until 10: ${range2.toList()}")
    println("10 downTo 1: ${range3.toList()}")
    
    // Step ranges
    val evenNumbers = 2..20 step 2
    println("Even numbers: ${evenNumbers.toList()}")
    
    val countdown = 10 downTo 0 step 2
    println("Countdown: ${countdown.toList()}")
    
    // Character ranges
    val alphabet = 'a'..'z'
    println("Alphabet contains 'm': ${'m' in alphabet}")
    
    // Using ranges in loops
    print("Counting: ")
    for (i in 1..5) {
        print("$i ")
    }
    println()
    
    // Range functions
    val numbers = listOf(3, 1, 4, 1, 5, 9, 2, 6)
    println("Numbers in range 2..5: ${numbers.filter { it in 2..5 }}")
    
    // Coerce values to range
    println("Coerce 15 to 1..10: ${15.coerceIn(1..10)}")
    println("Coerce -5 to 1..10: ${(-5).coerceIn(1..10)}")
}