Question

这是Kotlin中的一个简单泛型函数：

fun <T> twice(x: T) : T { return 2 * x }

尝试在项目或REPL中进行构建会导致以下错误：

error: none of the following functions can be called with the arguments supplied: 
public final operator fun times(other: Byte): Int defined in kotlin.Int
public final operator fun times(other: Double): Double defined in kotlin.Int
public final operator fun times(other: Float): Float defined in kotlin.Int
public final operator fun times(other: Int): Int defined in kotlin.Int
public final operator fun times(other: Long): Long defined in kotlin.Int
public final operator fun times(other: Short): Int defined in kotlin.Int
fun <T> twice(x: T) : T { return 2 * x }
                                   ^

如果将return语句操作数切换为x * 2，则错误消息变为：

error: unresolved reference. None of the following candidates is applicable because of receiver type mismatch: 
@InlineOnly public inline operator fun BigDecimal.times(other: BigDecimal): BigDecimal defined in kotlin
@InlineOnly public inline operator fun BigInteger.times(other: BigInteger): BigInteger defined in kotlin
fun <T> twice(x: T) : T { return x * 2 }
                                   ^

我在这里想念什么？

Answer 1

由于T可以是任何东西，因此编译器无法找到匹配的times运算符。正如您在错误消息中看到的那样，对于Int，有多种选择

public final operator fun times(other: Byte): Int defined in kotlin.Int
public final operator fun times(other: Double): Double defined in kotlin.Int
public final operator fun times(other: Float): Float defined in kotlin.Int
public final operator fun times(other: Int): Int defined in kotlin.Int
public final operator fun times(other: Long): Long defined in kotlin.Int
public final operator fun times(other: Short): Int defined in kotlin.Int

但是不幸的是，没有通用的times函数可以与例如Number。恐怕在这种情况下，您将不得不为要处理的每种类型创建重载，例如Double，Int等。

Kotlin中的简单泛型函数失败

1 个答案: