Kotlin 2.0 官方 Release Notes 深度拆解大典

参考官方文档: Kotlin 2.0.0 Released
Kotlin 2.0 是 JetBrains 团队划时代的里程碑版本。它全面默认启用了全新的 K2 编译器，编译速度提升 2 倍，并带来了 Smart Casts 2.0 (智能类型转换) 与改进的 Sealed Interfaces。

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🐳 容器运行环境 (Runtime Environment)

在固定版本 Docker 镜像 croquiscom/kotlin-base:2.0.10 中执行 Kotlin 编译器诊断：

📸 Unverified Snapshot📋croquiscom/kotlin-base:2.0.10

⏱️ 510msNot verified

openjdk version "21.0.11" 2026-04-21 LTS
OpenJDK Runtime Environment Temurin-21.0.11+10 (build 21.0.11+10-LTS)
OpenJDK 64-Bit Server VM Temurin-21.0.11+10 (build 21.0.11+10-LTS, mixed mode, sharing)

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1. 🧠 Smart Casts 2.0 (更智能的类型转换)

K2 编译器大大拓展了自动 Smart Cast 的上下文判别能力，在 when 逻辑分支和 is 检查后无需显式强转。

// 关联源码: demos/kotlin/kotlin2_demo.kt
sealed interface UserStatus {
    data class Active(val lastLogin: String) : UserStatus
    object Maintenance : UserStatus
}

val statusMsg = when (val s = user.status) {
    is UserStatus.Active -> "Active since ${s.lastLogin}"
    UserStatus.Maintenance -> "Under Maintenance"
}

📸 Unverified Snapshot📋eclipse-temurin:21-jdk-alpine

⏱️ 40msNot verified

Kotlin 2.0 Runtime Output:
User: Alice (ID: 101) -> Active since 2026-08-05