Kotlin 接收器名称冲突

Question

When running the following code snippet, the compiler is attempting to resolve the method isEmpty against a receiver defined in kotlin.collections for reasons I don't fully understand. The method isEmpty is defined within java.util.Optional . If I replace isEmpty with !isPresent , the code works as expected.

private fun getThreadCount(param: Optional<String>): Int {
        return if(param.isEmpty) {
            DEFAULT_THREAD_COUNT
        } else {
            val threads = param.get()
            try {
                threads.toInt()
            } catch (ex: NumberFormatException) {
                throw RuntimeException("Failed to parse threads parameter: $threads")
            }
        }
    }

> Task :compileKotlin FAILED
e: /home/.../TaskParams.kt: (51, 25): Function invocation 'isEmpty(...)' expected
e: /home/.../TaskParams.kt: (51, 25): Unresolved reference. None of the following 
candidates is applicable because of receiver type mismatch: 
public inline fun <T> Array<out ???>.isEmpty(): Boolean defined in kotlin.collections
public inline fun BooleanArray.isEmpty(): Boolean defined in kotlin.collections
public inline fun ByteArray.isEmpty(): Boolean defined in kotlin.collections
public inline fun CharArray.isEmpty(): Boolean defined in kotlin.collections
public inline fun CharSequence.isEmpty(): Boolean defined in kotlin.text
public inline fun DoubleArray.isEmpty(): Boolean defined in kotlin.collections
public inline fun FloatArray.isEmpty(): Boolean defined in kotlin.collections
public inline fun IntArray.isEmpty(): Boolean defined in kotlin.collections
public inline fun LongArray.isEmpty(): Boolean defined in kotlin.collections
public inline fun ShortArray.isEmpty(): Boolean defined in kotlin.collections

This is being compiled against Kotlin 1.3.72

Answer 1

java.util.Optional isEmpty() was added in Java 11. The Android version of Optional (or whatever your target is) does not have it.

Just go with the !isPresent() , or !isPresent with kotlin syntax sugar.