Kotlin中计算BigDecimal总和遇类型不匹配错误，求解决方案

错误原因 #

• 你定义的result是List<List<Any>>类型，每个子列表的第三个元素（索引2）已经是BigDecimal类型，无需再调用toBigDecimal()方法，这是导致接收者类型不匹配错误的直接原因。
• 额外注意：Data类的cost字段被定义为Int，但你赋值的是小数（如0.00000000001），这会直接导致精度丢失，必须修正字段类型。

修复方案 #

1. 修正Data类的cost字段类型 #

将cost: Int改为cost: Double，避免小数赋值给整数的精度问题：

data class Data(
  val id: Int,
  val cost: Double, // 修正为Double类型适配小数输入
  val env: String,
  val item: String
)

2. 修复总和计算代码 #

去掉多余的toBigDecimal()调用，同时用更简洁的sumOf替代forEach累加：

var totalCost: BigDecimal = BigDecimal.ZERO
result.forEach { totalCostData ->
    totalCost = totalCost.add(totalCostData[2] as BigDecimal)
}

3. 推荐的优化方案（类型更安全） #

直接在分组时生成TotalCost对象，避免Any类型的转换风险，后续操作更清晰：

data class Data(
  val id: Int,
  val cost: Double,
  val env: String,
  val item: String
)

data class TotalCost(
  val item: String,
  val env: String,
  val cost: BigDecimal
)

val input = listOf(
  Data(id = 1, cost = 0.00000000001, env = "prod", item = "Storage"),
  Data(id = 2, cost = 0.00000000002, env = "qa", item = "Storage"),
  Data(id = 3, cost = 0.00000000003, env = "prod", item = "Storage"),

  Data(id = 4, cost = 0.00000000005, env = "qa", item = "Bandwidth"),
  Data(id = 5, cost = 0.00000000002, env = "qa", item = "Bandwidth"),
  Data(id = 6, cost = 0.00000000005, env = "prod", item = "Bandwidth"),
  Data(id = 7, cost = 0.00000000006, env = "prod", item = "Bandwidth"),
  Data(id = 8, cost = 0.00000000001, env = "prod", item = "Bandwidth"),

  Data(id = 9, cost = 0.00000000005, env = "qa", item = "vm"),
  Data(id = 10, cost = 0.00000000002, env = "uat", item = "vm"),
  Data(id = 11, cost = 0.00000000003, env = "qa", item = "vm"),
  Data(id = 12, cost = 0.00000000004, env = "prod", item = "vm"),
  Data(id = 13, cost = 0.00000000005, env = "uat", item = "vm")
)

// 直接生成类型明确的TotalCost列表
val result = input
  .groupBy { it.item to it.env }
  .map { (key, value) ->
    TotalCost(
      item = key.first,
      env = key.second,
      cost = value.sumOf { it.cost.toBigDecimal() }
    )
  }

// 计算总和，无需类型转换
val totalCost = result.sumOf { it.cost }

内容的提问来源于stack exchange，提问作者user18282672