// 监听用户输入 → 请求搜索建议 → 过滤结果 → 更新 UI
searchBox.addTextChangedListener { text ->
    api.searchSuggestions(text.toString()) { result ->
        if (result.isSuccessful) {
            val filtered = result.body()?.filter { it.isNotEmpty() }
            if (filtered != null) {
                runOnUiThread {
                    adapter.submitList(filtered)
                }
            }
        }
    }
}

object StringUtils {
    fun isEmail(s: String): Boolean {
        return s.matches(Regex("^[\\w.-]+@[\\w.-]+\\.\\w+$"))
    }

    fun isEmpty(s: String?): Boolean {
        return s == null || s.isBlank()
    }

    fun truncate(s: String, maxLen: Int): String {
        return if (s.length > maxLen) s.take(maxLen) + "..." else s
    }
}

// 调用时
if (StringUtils.isEmail(input)) { ... }
val name = StringUtils.truncate(user.name, 20)

// 场景：创建一个用户对象并设置各种属性
val user = User()
user.name = "Alice"
user.age = 20
user.email = "alice@example.com"
user.city = "Beijing"

// 或者更糟：为了一个中间结果声明临时变量
val result = computeSomething()
val processed = process(result)
val finalValue = transform(processed)

val text = "Hello 🌍"
println(text.length) // 7？还是 8？
println(text[6])     // 期望拿到 🌍，实际是一个代理对的高位
println(text[7])     // 这才是代理对的低位

fun processOrder(order: Order) {
    val cart = order.cart
    // 移除库存不足的商品
    cart.items.filter { it.inStock }
    // 应用优惠券
    cart.total.applyDiscount(order.coupon)
    // 保存到数据库
    repository.save(cart)
}

sealed class Result
data class Success(val data: String) : Result()
data class Error(val message: String, val code: Int) : Result()
object Loading : Result()

fun handleResult(result: Result): String = when (result) {
    is Success -> "数据: ${result.data}"
    is Error -> "错误 ${result.code}: ${result.message}"
    is Loading -> "加载中..."
}

val config = mutableMapOf<String, String?>(
    "username" to "alice",
    "theme" to null  // 用户明确设置了 theme 为 null
)

// 问题：getOrDefault 无法区分"键不存在"和"值为 null"
val theme1 = config.getOrDefault("theme", "light")
println(theme1) // 输出: light ❌ 错误！用户明确设置了 null，应该保留 null

val theme2 = config.getOrDefault("language", "zh-CN")
println(theme2) // 输出: zh-CN ✅ 正确，键不存在时使用默认值

val names = listOf("Alice", "Bob", "Charlie")
val scores = mutableListOf(95, 87, 72)
val matrix = listOf(listOf(1, 0), listOf(0, 1))