Kotlin代码乘法操作编译报错，寻求原因及解决方法

我是Kotlin初学者，参考Android官方Codelab示例编写的单位转换代码无法编译，但示例代码可正常运行。相关代码及错误信息如下：

代码： #

package com.example.converterapp

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import com.example.converterapp.databinding.ActivityMainBinding

class MainActivity : AppCompatActivity() {

    lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
        binding.calculateButton.setOnClickListener{ calculate() }
    }

    fun calculate() {
        val stringInTextField = binding.measurementToConvert.text.toString()
        val measurement = stringInTextField.toDoubleOrNull()
        if (measurement == null) {
            binding.convertedMeasurement.text = ""
            return
        }

        val selectedId = binding.conversionOptions.checkedRadioButtonId
        val conversion = when (selectedId) {
            R.id.oz_to_cups -> 0.125
            R.id.cups_to_oz -> 8
            R.id.oz_to_grams -> 28.3495
            else -> 0.035274
        }
        var desiredMeasurement = measurement * conversion
        val roundUp = binding.roundUpSwitch.isChecked
        if (roundUp) {
            desiredMeasurement = kotlin.math.ceil(desiredMeasurement)
        }
        binding.convertedMeasurement.text = getString(R.string.convertedMeasurement, desiredMeasurement)
    }

}

错误信息： #

\ConverterApp\app\src\main\java\com\example\converterapp\MainActivity.kt: (33, 46): None of the following functions can be called with the arguments supplied: 
public final operator fun times(other: Byte): Double defined in kotlin.Double
public final operator fun times(other: Double): Double defined in kotlin.Double
public final operator fun times(other: Float): Double defined in kotlin.Double
public final operator fun times(other: Int): Double defined in kotlin.Double
public final operator fun times(other: Long): Double defined in kotlin.Double
public final operator fun times(other: Short): Double defined in kotlin.Double

原因分析： #

编译错误出现在measurement * conversion这一行。问题在于conversion变量的类型推断：when表达式中，R.id.cups_to_oz -> 8返回的是Int类型，而其他分支返回的是Double类型。Kotlin会把conversion的类型推断为Number（所有数值类型的父类），但Double的times方法（即乘法运算符）不接受Number类型的参数，因此触发编译错误。

解决方法： #

把when表达式中所有分支的数值统一改为Double类型，确保conversion被推断为Double。只需要把8改成8.0即可：

val conversion = when (selectedId) {
    R.id.oz_to_cups -> 0.125
    R.id.cups_to_oz -> 8.0  // 改为Double类型
    R.id.oz_to_grams -> 28.3495
    else -> 0.035274
}

修改后，conversion的类型会被正确推断为Double，就能和measurement（Double类型）正常执行乘法运算了。

内容的提问来源于stack exchange，提问作者Moya.A