refactor: use objects instead of managing singletons manually

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/Parser.kt

@@ -35,11 +35,7 @@ public abstract class Parser(input: TokenStream) : Recognizer<Token, ParserATNSi
     }
   }
 
-  public class TrimToSizeListener : ParseTreeListener {
-    public companion object {
-      public val INSTANCE: TrimToSizeListener = TrimToSizeListener()
-    }
-
+  public object TrimToSizeListener : ParseTreeListener {
     override fun enterEveryRule(ctx: ParserRuleContext) {
       // Noop
     }
@@ -143,16 +139,16 @@ public abstract class Parser(input: TokenStream) : Recognizer<Token, ParserATNSi
    * This property is set to `false` by default for a newly constructed parser.
    */
   public var trimParseTree: Boolean
-    get() = parseListeners.contains(TrimToSizeListener.INSTANCE)
+    get() = parseListeners.contains(TrimToSizeListener)
     set(value) {
       if (value) {
         if (trimParseTree) {
           return
         }
 
-        addParseListener(TrimToSizeListener.INSTANCE)
+        addParseListener(TrimToSizeListener)
       } else {
-        removeParseListener(TrimToSizeListener.INSTANCE)
+        removeParseListener(TrimToSizeListener)
       }
     }
 

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/atn/ATNConfig.kt

@@ -95,7 +95,7 @@ public open class ATNConfig {
     state: ATNState,
     alt: Int,
     context: PredictionContext?,
-    semanticContext: SemanticContext = SemanticContext.Empty.Instance,
+    semanticContext: SemanticContext = SemanticContext.Empty,
   ) {
     this.state = state
     this.alt = alt
@@ -181,7 +181,7 @@ public open class ATNConfig {
       buf.append("]")
     }
 
-    if (semanticContext !== SemanticContext.Empty.Instance) {
+    if (semanticContext !== SemanticContext.Empty) {
       buf.append(",")
       buf.append(semanticContext)
     }

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/atn/ATNConfigSet.kt

@@ -26,13 +26,9 @@ public open class ATNConfigSet(public val fullCtx: Boolean = true) : MutableSet<
    * the number of objects associated with ATNConfigs. The other solution is to
    * use a hash table that lets us specify the equals/hashcode operation.
    */
-  public class ConfigHashSet : AbstractConfigHashSet(ConfigEqualityComparator.INSTANCE)
-
-  public class ConfigEqualityComparator private constructor() : AbstractEqualityComparator<ATNConfig>() {
-    public companion object {
-      public val INSTANCE: ConfigEqualityComparator = ConfigEqualityComparator()
-    }
+  public class ConfigHashSet : AbstractConfigHashSet(ConfigEqualityComparator)
 
+  public object ConfigEqualityComparator : AbstractEqualityComparator<ATNConfig>() {
     override fun hashCode(obj: ATNConfig): Int {
       var hashCode = 7
       hashCode = 31 * hashCode + obj.state.stateNumber
@@ -50,9 +46,9 @@ public open class ATNConfigSet(public val fullCtx: Boolean = true) : MutableSet<
         return false
       }
 
-      return a.state.stateNumber == b.state.stateNumber &&
-        a.alt == b.alt &&
-        a.semanticContext == b.semanticContext
+      return a.state.stateNumber == b.state.stateNumber
+        && a.alt == b.alt
+        && a.semanticContext == b.semanticContext
     }
   }
 
@@ -119,7 +115,7 @@ public open class ATNConfigSet(public val fullCtx: Boolean = true) : MutableSet<
       val preds = ArrayList<SemanticContext>()
 
       for (c in configs) {
-        if (c.semanticContext !== SemanticContext.Empty.Instance) {
+        if (c.semanticContext !== SemanticContext.Empty) {
           preds.add(c.semanticContext)
         }
       }
@@ -171,7 +167,7 @@ public open class ATNConfigSet(public val fullCtx: Boolean = true) : MutableSet<
       throw IllegalStateException("This set is readonly")
     }
 
-    if (config.semanticContext !== SemanticContext.Empty.Instance) {
+    if (config.semanticContext !== SemanticContext.Empty) {
       hasSemanticContext = true
     }
 

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/atn/ATNDeserializer.kt

@@ -525,10 +525,10 @@ public open class ATNDeserializer(private val deserializationOptions: ATNDeseria
       LexerActionType.CHANNEL -> LexerChannelAction(data1)
       LexerActionType.CUSTOM -> LexerCustomAction(data1, data2)
       LexerActionType.MODE -> LexerModeAction(data1)
-      LexerActionType.MORE -> LexerMoreAction.INSTANCE
-      LexerActionType.POP_MODE -> LexerPopModeAction.INSTANCE
+      LexerActionType.MORE -> LexerMoreAction
+      LexerActionType.POP_MODE -> LexerPopModeAction
       LexerActionType.PUSH_MODE -> LexerPushModeAction(data1)
-      LexerActionType.SKIP -> LexerSkipAction.INSTANCE
+      LexerActionType.SKIP -> LexerSkipAction
       LexerActionType.TYPE -> LexerTypeAction(data1)
     }
 

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/atn/EmptyPredictionContext.kt

@@ -1,21 +1,8 @@
 // Copyright 2017-present Strumenta and contributors, licensed under Apache 2.0.
 // Copyright 2024-present Strumenta and contributors, licensed under BSD 3-Clause.
-
 package org.antlr.v4.kotlinruntime.atn
 
-import kotlin.jvm.JvmStatic
-
-@Suppress("EqualsOrHashCode")
-public class EmptyPredictionContext : SingletonPredictionContext(null, EMPTY_RETURN_STATE) {
-  public companion object {
-    /**
-     * Represents `$` in local context prediction, which means wildcard.
-     * `*+x = *`.
-     */
-    @JvmStatic
-    public val Instance: EmptyPredictionContext = EmptyPredictionContext()
-  }
-
+public object EmptyPredictionContext : SingletonPredictionContext(null, EMPTY_RETURN_STATE) {
   override val isEmpty: Boolean =
     true
 

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/atn/LL1Analyzer.kt

@@ -48,7 +48,7 @@ public open class LL1Analyzer(public val atn: ATN) {
       _LOOK(
         s = s.transition(alt).target,
         stopState = null,
-        ctx = EmptyPredictionContext.Instance,
+        ctx = EmptyPredictionContext,
         look = look[alt]!!,
         lookBusy = lookBusy,
         calledRuleStack = BitSet(),
@@ -192,7 +192,7 @@ public open class LL1Analyzer(public val atn: ATN) {
         return
       }
 
-      if (ctx !== EmptyPredictionContext.Instance) {
+      if (ctx !== EmptyPredictionContext) {
         // Run through all possible stack tops in ctx
         val removed = calledRuleStack.get(s.ruleIndex)
 

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/atn/LexerATNConfig.kt

@@ -20,7 +20,7 @@ public class LexerATNConfig : ATNConfig {
     state: ATNState,
     alt: Int,
     context: PredictionContext,
-  ) : super(state, alt, context, SemanticContext.Empty.Instance) {
+  ) : super(state, alt, context, SemanticContext.Empty) {
     passedThroughNonGreedyDecision = false
     lexerActionExecutor = null
   }
@@ -30,7 +30,7 @@ public class LexerATNConfig : ATNConfig {
     alt: Int,
     context: PredictionContext,
     lexerActionExecutor: LexerActionExecutor,
-  ) : super(state, alt, context, SemanticContext.Empty.Instance) {
+  ) : super(state, alt, context, SemanticContext.Empty) {
     this.lexerActionExecutor = lexerActionExecutor
     passedThroughNonGreedyDecision = false
   }
@@ -89,7 +89,7 @@ public class LexerATNConfig : ATNConfig {
       return false
     }
 
-    if (!ObjectEqualityComparator.INSTANCE.equals(lexerActionExecutor, other.lexerActionExecutor)) {
+    if (!ObjectEqualityComparator.equals(lexerActionExecutor, other.lexerActionExecutor)) {
       return false
     }
 

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/atn/LexerATNSimulator.kt

@@ -403,7 +403,7 @@ public open class LexerATNSimulator(
     }
 
   protected open fun computeStartState(input: CharStream, p: ATNState): ATNConfigSet {
-    val initialContext = EmptyPredictionContext.Instance
+    val initialContext = EmptyPredictionContext
     val configs = OrderedATNConfigSet()
 
     for (i in 0..<p.numberOfTransitions) {
@@ -460,7 +460,7 @@ public open class LexerATNSimulator(
           return true
         }
 
-        configs.add(LexerATNConfig(config, config.state, EmptyPredictionContext.Instance))
+        configs.add(LexerATNConfig(config, config.state, EmptyPredictionContext))
         tempCurrentAltReachedAcceptState = true
       }
 

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/atn/LexerMoreAction.kt

@@ -1,29 +1,20 @@
 // Copyright 2017-present Strumenta and contributors, licensed under Apache 2.0.
 // Copyright 2024-present Strumenta and contributors, licensed under BSD 3-Clause.
-
 package org.antlr.v4.kotlinruntime.atn
 
 import org.antlr.v4.kotlinruntime.Lexer
-import org.antlr.v4.kotlinruntime.atn.LexerMoreAction.Companion.INSTANCE
 import org.antlr.v4.kotlinruntime.misc.MurmurHash
 
 /**
  * Implements the `more` lexer action by calling [Lexer.more].
  *
- * The `more` command does not have any parameters, so this action is
- * implemented as a singleton instance exposed by [INSTANCE].
+ * The `more` command does not have any parameters,
+ * so this action is implemented as an object.
  *
  * @author Sam Harwell
  * @since 4.2
  */
-public class LexerMoreAction private constructor() : LexerAction {
-  public companion object {
-    /**
-     * Provides a singleton instance of this parameterless lexer action.
-     */
-    public val INSTANCE: LexerMoreAction = LexerMoreAction()
-  }
-
+public object LexerMoreAction : LexerAction {
   /**
    * Returns [LexerActionType.MORE].
    */

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/atn/LexerPopModeAction.kt

@@ -1,29 +1,20 @@
 // Copyright 2017-present Strumenta and contributors, licensed under Apache 2.0.
 // Copyright 2024-present Strumenta and contributors, licensed under BSD 3-Clause.
-
 package org.antlr.v4.kotlinruntime.atn
 
 import org.antlr.v4.kotlinruntime.Lexer
-import org.antlr.v4.kotlinruntime.atn.LexerPopModeAction.Companion.INSTANCE
 import org.antlr.v4.kotlinruntime.misc.MurmurHash
 
 /**
  * Implements the `popMode` lexer action by calling [Lexer.popMode].
  *
- * The `popMode` command does not have any parameters, so this action is
- * implemented as a singleton instance exposed by [INSTANCE].
+ * The `popMode` command does not have any parameters,
+ * so this action is implemented as an object.
  *
  * @author Sam Harwell
  * @since 4.2
  */
-public class LexerPopModeAction private constructor() : LexerAction {
-  public companion object {
-    /**
-     * Provides a singleton instance of this parameterless lexer action.
-     */
-    public val INSTANCE: LexerPopModeAction = LexerPopModeAction()
-  }
-
+public object LexerPopModeAction : LexerAction {
   /**
    * Returns [LexerActionType.POP_MODE].
    */

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/atn/LexerSkipAction.kt

@@ -1,29 +1,20 @@
 // Copyright 2017-present Strumenta and contributors, licensed under Apache 2.0.
 // Copyright 2024-present Strumenta and contributors, licensed under BSD 3-Clause.
-
 package org.antlr.v4.kotlinruntime.atn
 
 import org.antlr.v4.kotlinruntime.Lexer
-import org.antlr.v4.kotlinruntime.atn.LexerSkipAction.Companion.INSTANCE
 import org.antlr.v4.kotlinruntime.misc.MurmurHash
 
 /**
  * Implements the `skip` lexer action by calling [Lexer.skip].
  *
- * The `skip` command does not have any parameters, so this action is
- * implemented as a singleton instance exposed by [INSTANCE].
+ * The `skip` command does not have any parameters,
+ * so this action is implemented as an object.
  *
  * @author Sam Harwell
  * @since 4.2
  */
-public class LexerSkipAction private constructor() : LexerAction {
-  public companion object {
-    /**
-     * Provides a singleton instance of this parameterless lexer action.
-     */
-    public val INSTANCE: LexerSkipAction = LexerSkipAction()
-  }
-
+public object LexerSkipAction : LexerAction {
   /**
    * Returns [LexerActionType.SKIP].
    */

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/atn/OrderedATNConfigSet.kt

@@ -9,7 +9,7 @@ import org.antlr.v4.kotlinruntime.misc.ObjectEqualityComparator
  * @author Sam Harwell
  */
 public class OrderedATNConfigSet : ATNConfigSet() {
-  public class LexerConfigHashSet : AbstractConfigHashSet(ObjectEqualityComparator.INSTANCE)
+  public class LexerConfigHashSet : AbstractConfigHashSet(ObjectEqualityComparator)
 
   init {
     configLookup = LexerConfigHashSet()

antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/atn/ParserATNSimulator.kt

@@ -1210,8 +1210,8 @@ public open class ParserATNSimulator(
 
     for (i in 1..nAlts) {
       if (altToPred[i] == null) {
-        altToPred[i] = SemanticContext.Empty.Instance
-      } else if (altToPred[i] !== SemanticContext.Empty.Instance) {
+        altToPred[i] = SemanticContext.Empty
+      } else if (altToPred[i] !== SemanticContext.Empty) {
         nPredAlts++
       }
     }
@@ -1249,7 +1249,7 @@ public open class ParserATNSimulator(
         pairs.add(DFAState.PredPrediction(pred, i))
       }
 
-      if (pred !== SemanticContext.Empty.Instance) {
+      if (pred !== SemanticContext.Empty) {
         containsPredicate = true
       }
     }
@@ -1362,7 +1362,7 @@ public open class ParserATNSimulator(
     val failed = ATNConfigSet(configs.fullCtx)
 
     for (c in configs) {
-      if (c.semanticContext !== SemanticContext.Empty.Instance) {
+      if (c.semanticContext !== SemanticContext.Empty) {
         val predicateEvaluationResult = evalSemanticContext(c.semanticContext, outerContext, c.alt, configs.fullCtx)
 
         if (predicateEvaluationResult) {
@@ -1396,7 +1396,7 @@ public open class ParserATNSimulator(
     val predictions = BitSet()
 
     for (pair in predPredictions) {
-      if (pair.pred === SemanticContext.Empty.Instance) {
+      if (pair.pred === SemanticContext.Empty) {
         predictions.set(pair.alt)
 
         if (!complete) {
@@ -1511,7 +1511,7 @@ public open class ParserATNSimulator(
         for (i in 0..<config.context!!.size()) {
           if (config.context!!.getReturnState(i) == PredictionContext.EMPTY_RETURN_STATE) {
             if (fullCtx) {
-              configs.add(ATNConfig(config, config.state, EmptyPredictionContext.Instance), mergeCache)
+              configs.add(ATNConfig(config, config.state, EmptyPredictionContext), mergeCache)
               continue
             }