Kotlin Language Specification

// kotlin_language_specification.kt
// Demonstrasi beberapa perilaku yang diatur oleh Kotlin Language Specification
// (https://kotlinlang.org/spec/).
// Spec menjelaskan aturan resolusi overloading, smart cast, dan inferensi tipe
// secara formal.

// 1. Smart cast — spec menjelaskan kapan smart cast berlaku
fun smartCastDemo(x: Any): String {
    if (x is String) {
        // Smart cast otomatis ke String; spec bagian 11.1.1
        return x.uppercase()
    }
    return "bukan string"
}

// 2. Operator overloading — spec bagian 13 (Operator functions)
data class Vektor(val x: Int, val y: Int) {
    operator fun plus(other: Vektor) = Vektor(x + other.x, y + other.y)
    operator fun times(skalor: Int) = Vektor(x * skalor, y * skalor)
}

// 3. Resolution ambiguity — spec bagian 11 (Overload resolution)
class Layanan {
    fun panggil(x: Int) = "int"
    fun panggil(x: String) = "string"
    fun panggil(x: Any) = "any"
}

// 4. Default argument — spec bagian 8.5.1 (Default values)
fun buatNama(depan: String = "Tanpa", belakang: String = "Nama") =
    "$depan $belakang"

// 5. Elaborasi tipe nullable — spec bagian 7.1 (Nullability)
fun panjangNullable(s: String?): Int = s?.length ?: 0

fun main() {
    println("=== Kotlin Language Specification ===")
    println("Sumber resmi: https://kotlinlang.org/spec/")
    println()

    println("--- 1. Smart cast (spec 11.1.1) ---")
    println("smartCastDemo(\"halo\")  -> ${smartCastDemo("halo")}")
    println("smartCastDemo(42)      -> ${smartCastDemo(42)}")

    println()
    println("--- 2. Operator overloading (spec 13) ---")
    val a = Vektor(1, 2)
    val b = Vektor(3, 4)
    println("a + b = ${a + b}")
    println("a * 5 = ${a * 5}")

    println()
    println("--- 3. Overload resolution (spec 11) ---")
    val l = Layanan()
    println("panggil(42)       -> ${l.panggil(42)}")        // int (paling spesifik)
    println("panggil(\"halo\")   -> ${l.panggil("halo")}")  // string (paling spesifik)
    println("panggil(true)     -> ${l.panggil(true)}")      // any (fallback)

    println()
    println("--- 4. Default argument (spec 8.5.1) ---")
    println("buatNama()                 -> ${buatNama()}")
    println("buatNama(\"Budi\")            -> ${buatNama("Budi")}")
    println("buatNama(\"Siti\", \"Dewi\")    -> ${buatNama("Siti", "Dewi")}")
    println("buatNama(belakang=\"X\")      -> ${buatNama(belakang = "X")}")

    println()
    println("--- 5. Nullability (spec 7.1) ---")
    println("panjangNullable(\"halo\") -> ${panjangNullable("halo")}")
    println("panjangNullable(null)   -> ${panjangNullable(null)}")

    println()
    println("--- 6. Bagian utama spec ---")
    val bagian = listOf(
        "1. Introduction — tujuan dan struktur spec",
        "2. Lexical grammar — token, identifier, literal",
        "3. Type system — tipe data, nullability, generic",
        "4. Expressions — operator, lambda, when, try",
        "5. Declarations — class, function, property, import",
        "6. Statements — assignment, control flow",
        "7. Resolution — overload, smart cast, type inference",
        "8. Patterns — destructuring, builder"
    )
    bagian.forEach { println("  $it") }

    println()
    println("--- 7. Cara membaca spec ---")
    println("  Spec ditulis dalam Markdown berisi aturan formal (kadang BNF)")
    println("  Tidak semua section relevan untuk sehari-hari; fokus ke bagian")
    println("  yang menjelaskan perilaku membingungkan (smart cast, overload)")
}

=== Kotlin Language Specification ===
Sumber resmi: https://kotlinlang.org/spec/

--- 1. Smart cast (spec 11.1.1) ---
smartCastDemo("halo")  -> HALO
smartCastDemo(42)      -> bukan string

--- 2. Operator overloading (spec 13) ---
a + b = Vektor(x=4, y=6)
a * 5 = Vektor(x=5, y=10)

--- 3. Overload resolution (spec 11) ---
panggil(42)       -> int
panggil("halo")   -> string
panggil(true)     -> any

--- 4. Default argument (spec 8.5.1) ---
buatNama()                 -> Tanpa Nama
buatNama("Budi")            -> Budi Nama
buatNama("Siti", "Dewi")    -> Siti Dewi
buatNama(belakang="X")      -> Tanpa X

--- 5. Nullability (spec 7.1) ---
panjangNullable("halo") -> 4
panjangNullable(null)   -> 0

--- 6. Bagian utama spec ---
  1. Introduction — tujuan dan struktur spec
  2. Lexical grammar — token, identifier, literal
  3. Type system — tipe data, nullability, generic
  4. Expressions — operator, lambda, when, try
  5. Declarations — class, function, property, import
  6. Statements — assignment, control flow
  7. Resolution — overload, smart cast, type inference
  8. Patterns — destructuring, builder

--- 7. Cara membaca spec ---
  Spec ditulis dalam Markdown berisi aturan formal (kadang BNF)
  Tidak semua section relevan untuk sehari-hari; fokus ke bagian
  yang menjelaskan perilaku membingungkan (smart cast, overload)