How do you access a named group in Kotlin?

named-match-repro.kts

#!/usr/bin/env kotlinc -script --
/**
 @file named-match-repro.kts
 @author Jeremy W. Sherman (GitHub: @jeremy-w)

 Demo of some perplexing behavior.

 Questions:

 - Main question: How do I access a named capture group in a Kotlin script?
 - Follow-up questions:
     - How does the safe-cast to MatchNamedGroupCollection succeed, but then
       explode on trying to use the named-group feature?
       (see sample log at end of file)
     - How is it that the Pattern handles the named group fine, but I can't
       actually get the group by name?

 Relevant versions:

    > kotlinc -version
    info: kotlinc-jvm 1.3.0 (JRE 1.8.0_144-b01)
    > javac -version
    javac 1.8.0_144
    > sw_vers
    ProductName:    Mac OS X
    ProductVersion: 10.13.6
    BuildVersion:   17G3025
    > uname -a
    Darwin Eclipse.local 17.7.0 Darwin Kernel Version 17.7.0: Wed Oct 10
    23:06:14 PDT 2018; root:xnu-4570.71.13~1/RELEASE_X86_64 x86_64
*/

import kotlin.system.exitProcess

val input = args.firstOrNull() ?: "abc123xyz456"

val numbersRegex = Regex("""(?<number>\d+)""")
val matches = numbersRegex.findAll(input).toList()
println("There are ${matches.size} numbers in \"$input\":")

for (match in matches) {
    val numberGroup =
        try {
            (match.groups as? MatchNamedGroupCollection)?.let {
                        println("DEBUG: MatchNamedGroupCollection: implementsMatchNamedGroupCollection=${it::class is MatchNamedGroupCollection} it=$it")
                        println("See that \"false\"? How the heck did that safe-cast succeed?!")
                        it.get("number")
                    }
        } catch(t: Throwable) {
            println("ERROR: NamedGroup failed: $t")
            t.printStackTrace()

            println("\nFalling back on numbered groups.")
            null
        }
        ?:
        match.groups.get(1)
    numberGroup?.let {
        val number = it.value
        println("$number")
    }
}


/*
Sample run:

> ./named-match-repro.kts abc123
There are 1 numbers in "abc123":
DEBUG: MatchNamedGroupCollection: implementsMatchNamedGroupCollection=false it=[MatchGroup(value=123, range=3..5), MatchGroup(value=123, range=3..5)]
See that "false"? How the heck did that safe-cast succeed?!
ERROR: NamedGroup failed: java.lang.UnsupportedOperationException: Retrieving groups by name is not supported on this platform.
java.lang.UnsupportedOperationException: Retrieving groups by name is not supported on this platform.
        at kotlin.internal.PlatformImplementations.getMatchResultNamedGroup(PlatformImplementations.kt:20)
        at kotlin.text.MatcherMatchResult$groups$1.get(Regex.kt:290)
        at Named_match_repro.<init>(named-match-repro.kts:17)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
        at org.jetbrains.kotlin.script.ReflectionUtilKt.tryConstructClassFromStringArgs(reflectionUtil.kt:27)
        at org.jetbrains.kotlin.cli.jvm.compiler.KotlinToJVMBytecodeCompiler.compileAndExecuteScript$cli(KotlinToJVMBytecodeCompiler.kt:263)
        at org.jetbrains.kotlin.cli.jvm.K2JVMCompiler.doExecute(K2JVMCompiler.kt:182)
        at org.jetbrains.kotlin.cli.jvm.K2JVMCompiler.doExecute(K2JVMCompiler.kt:57)
        at org.jetbrains.kotlin.cli.common.CLICompiler.execImpl(CLICompiler.java:96)
        at org.jetbrains.kotlin.cli.common.CLICompiler.execImpl(CLICompiler.java:52)
        at org.jetbrains.kotlin.cli.common.CLITool.exec(CLITool.kt:93)
        at org.jetbrains.kotlin.cli.common.CLITool.exec(CLITool.kt:71)
        at org.jetbrains.kotlin.cli.common.CLITool.exec(CLITool.kt:39)
        at org.jetbrains.kotlin.cli.common.CLITool$Companion.doMainNoExit(CLITool.kt:202)
        at org.jetbrains.kotlin.cli.common.CLITool$Companion.doMain(CLITool.kt:194)
        at org.jetbrains.kotlin.cli.jvm.K2JVMCompiler$Companion.main(K2JVMCompiler.kt:350)
        at org.jetbrains.kotlin.cli.jvm.K2JVMCompiler.main(K2JVMCompiler.kt)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.jetbrains.kotlin.preloading.Preloader.run(Preloader.java:81)
        at org.jetbrains.kotlin.preloading.Preloader.main(Preloader.java:43)

Falling back on numbered groups.
123
*/

This appears to be a known issue: https://youtrack.jetbrains.com/issue/KT-20865

But there, they're talking about it being broken on Java 9, while I'm running Java 8 at the moment… 🤔