Use abstract readonly collections as base classes for implementing collection properties of regex MatchResult

js/js.libraries/src/core/regex.kt

@@ -197,15 +197,9 @@ private fun RegExp.findNext(input: String, from: Int): MatchResult? {
         override val value: String
             get() = match[0]!!
 
-        override val groups: MatchGroupCollection = object : MatchGroupCollection {
+        override val groups: MatchGroupCollection = object : MatchGroupCollection, AbstractCollection<MatchGroup?>() {
             override val size: Int get() = match.length
-            override fun isEmpty(): Boolean = size == 0
-
-            override fun contains(element: MatchGroup?): Boolean = this.any { it == element }
-            override fun containsAll(elements: Collection<MatchGroup?>): Boolean = elements.all { contains(it) }
-
             override fun iterator(): Iterator<MatchGroup?> = indices.asSequence().map { this[it] }.iterator()
-
             override fun get(index: Int): MatchGroup? = match[index]?.let { MatchGroup(it) }
         }
 

libraries/stdlib/src/kotlin/text/regex/Regex.kt

@@ -16,7 +16,8 @@
 @file:JvmVersion
 package kotlin.text
 
-import java.util.*
+import java.util.Collections
+import java.util.EnumSet
 import java.util.regex.Matcher
 import java.util.regex.Pattern
 import kotlin.internal.IMPLEMENTATIONS
@@ -232,11 +233,9 @@ private class MatcherMatchResult(private val matcher: Matcher, private val input
     override val value: String
         get() = matchResult.group()
 
-    override val groups: MatchGroupCollection = object : MatchNamedGroupCollection {
+    override val groups: MatchGroupCollection = object : MatchNamedGroupCollection, AbstractCollection<MatchGroup?>() {
         override val size: Int get() = matchResult.groupCount() + 1
         override fun isEmpty(): Boolean = false
-        override fun contains(element: MatchGroup?): Boolean = this.any { it == element }
-        override fun containsAll(elements: Collection<MatchGroup?>): Boolean = elements.all { contains(it) }
 
         override fun iterator(): Iterator<MatchGroup?> = indices.asSequence().map { this[it] }.iterator()
         override fun get(index: Int): MatchGroup? {