diff --git a/runtime/Swift/Sources/Antlr4/CommonTokenStream.swift b/runtime/Swift/Sources/Antlr4/CommonTokenStream.swift
index 8abaac82d8..c1ae934763 100644
--- a/runtime/Swift/Sources/Antlr4/CommonTokenStream.swift
+++ b/runtime/Swift/Sources/Antlr4/CommonTokenStream.swift
@@ -121,9 +121,7 @@ public class CommonTokenStream: BufferedTokenStream {
     public func getNumberOfOnChannelTokens() throws -> Int {
         var n = 0
         try fill()
-        let length = tokens.count
-        for i in 0..<length {
-            let t = tokens[i]
+        for t in tokens {
             if t.getChannel() == channel {
                 n += 1
             }
diff --git a/runtime/Swift/Sources/Antlr4/Parser.swift b/runtime/Swift/Sources/Antlr4/Parser.swift
index db27484554..0cd08494dc 100644
--- a/runtime/Swift/Sources/Antlr4/Parser.swift
+++ b/runtime/Swift/Sources/Antlr4/Parser.swift
@@ -378,12 +378,9 @@ open class Parser: Recognizer<ParserATNSimulator> {
     public func triggerExitRuleEvent() throws {
         // reverse order walk of listeners
         if let _parseListeners = _parseListeners, let _ctx = _ctx {
-            var i = _parseListeners.count - 1
-            while i >= 0 {
-                let listener = _parseListeners[i]
+            for listener in _parseListeners.reversed() {
                 _ctx.exitRule(listener)
                 try listener.exitEveryRule(_ctx)
-                i -= 1
             }
         }
     }
diff --git a/runtime/Swift/Sources/Antlr4/atn/ATNConfigSet.swift b/runtime/Swift/Sources/Antlr4/atn/ATNConfigSet.swift
index 30dda79bb5..5d940a3ea0 100644
--- a/runtime/Swift/Sources/Antlr4/atn/ATNConfigSet.swift
+++ b/runtime/Swift/Sources/Antlr4/atn/ATNConfigSet.swift
@@ -292,11 +292,10 @@ public final class ATNConfigSet: Hashable, CustomStringConvertible {
     }
 
     public func getConflictingAltSubsets() -> [BitSet] {
-        let length = configs.count
         var configToAlts = [Int: BitSet]()
 
-        for i in 0..<length {
-            let hash = configHash(configs[i].state.stateNumber, configs[i].context)
+        for cfg in configs {
+            let hash = configHash(cfg.state.stateNumber, cfg.context)
             var alts: BitSet
             if let configToAlt = configToAlts[hash] {
                 alts = configToAlt
@@ -305,26 +304,25 @@ public final class ATNConfigSet: Hashable, CustomStringConvertible {
                 configToAlts[hash] = alts
             }
 
-            try! alts.set(configs[i].alt)
+            try! alts.set(cfg.alt)
         }
 
         return Array(configToAlts.values)
     }
 
     public func getStateToAltMap() -> [Int: BitSet] {
-        let length = configs.count
         var m = [Int: BitSet]()
 
-        for i in 0..<length {
+        for cfg in configs {
             var alts: BitSet
-            if let mAlts =  m[configs[i].state.stateNumber] {
+            if let mAlts =  m[cfg.state.stateNumber] {
                 alts = mAlts
             } else {
                 alts = BitSet()
-                m[configs[i].state.stateNumber] = alts
+                m[cfg.state.stateNumber] = alts
             }
 
-            try! alts.set(configs[i].alt)
+            try! alts.set(cfg.alt)
         }
         return m
     }
diff --git a/runtime/Swift/Sources/Antlr4/atn/ArrayPredictionContext.swift b/runtime/Swift/Sources/Antlr4/atn/ArrayPredictionContext.swift
index 4257ec95c5..edfdb3a767 100644
--- a/runtime/Swift/Sources/Antlr4/atn/ArrayPredictionContext.swift
+++ b/runtime/Swift/Sources/Antlr4/atn/ArrayPredictionContext.swift
@@ -84,8 +84,8 @@ public class ArrayPredictionContext: PredictionContext {
         let length = parents.count
         var uniqueParents: Dictionary<PredictionContext, PredictionContext> =
         Dictionary<PredictionContext, PredictionContext>()
-        for p in 0..<length {
-            if let parent: PredictionContext = parents[p] {
+        for p in parents {
+            if let parent: PredictionContext = p {
                 // if !uniqueParents.keys.contains(parent) {
                 if uniqueParents[parent] == nil {
                     uniqueParents[parent] = parent  // don't replace
diff --git a/runtime/Swift/Sources/Antlr4/atn/ParseInfo.swift b/runtime/Swift/Sources/Antlr4/atn/ParseInfo.swift
index 2eb4045927..ccac60b088 100644
--- a/runtime/Swift/Sources/Antlr4/atn/ParseInfo.swift
+++ b/runtime/Swift/Sources/Antlr4/atn/ParseInfo.swift
@@ -61,9 +61,8 @@ public class ParseInfo {
     public func getTotalTimeInPrediction() -> Int64 {
         let decisions: [DecisionInfo] = atnSimulator.getDecisionInfo()
         var t: Int64 = 0
-        let length = decisions.count
-        for i in 0..<length {
-            t += decisions[i].timeInPrediction
+        for d in decisions {
+            t += d.timeInPrediction
         }
         return t
     }
@@ -76,9 +75,8 @@ public class ParseInfo {
     public func getTotalSLLLookaheadOps() -> Int64 {
         let decisions: [DecisionInfo] = atnSimulator.getDecisionInfo()
         var k: Int64 = 0
-        let length = decisions.count
-        for i in 0..<length {
-            k += decisions[i].SLL_TotalLook
+        for d in decisions {
+            k += d.SLL_TotalLook
         }
         return k
     }
@@ -91,9 +89,8 @@ public class ParseInfo {
     public func getTotalLLLookaheadOps() -> Int64 {
         let decisions: [DecisionInfo] = atnSimulator.getDecisionInfo()
         var k: Int64 = 0
-        let length = decisions.count
-        for i in 0..<length {
-            k += decisions[i].LL_TotalLook
+        for d in decisions {
+            k += d.LL_TotalLook
         }
         return k
     }
@@ -105,9 +102,8 @@ public class ParseInfo {
     public func getTotalSLLATNLookaheadOps() -> Int64 {
         let decisions: [DecisionInfo] = atnSimulator.getDecisionInfo()
         var k: Int64 = 0
-        let length = decisions.count
-        for i in 0..<length {
-            k += decisions[i].SLL_ATNTransitions
+        for d in decisions {
+            k += d.SLL_ATNTransitions
         }
         return k
     }
@@ -119,9 +115,8 @@ public class ParseInfo {
     public func getTotalLLATNLookaheadOps() -> Int64 {
         let decisions: [DecisionInfo] = atnSimulator.getDecisionInfo()
         var k: Int64 = 0
-        let length = decisions.count
-        for i in 0..<length {
-            k += decisions[i].LL_ATNTransitions
+        for d in decisions {
+            k += d.LL_ATNTransitions
         }
         return k
     }
@@ -137,10 +132,9 @@ public class ParseInfo {
     public func getTotalATNLookaheadOps() -> Int64 {
         let decisions: [DecisionInfo] = atnSimulator.getDecisionInfo()
         var k: Int64 = 0
-        let length = decisions.count
-        for i in 0..<length {
-            k += decisions[i].SLL_ATNTransitions
-            k += decisions[i].LL_ATNTransitions
+        for d in decisions {
+            k += d.SLL_ATNTransitions
+            k += d.LL_ATNTransitions
         }
         return k
     }
diff --git a/runtime/Swift/Sources/Antlr4/atn/ParserATNSimulator.swift b/runtime/Swift/Sources/Antlr4/atn/ParserATNSimulator.swift
index d3fb8342bf..d3cffff196 100644
--- a/runtime/Swift/Sources/Antlr4/atn/ParserATNSimulator.swift
+++ b/runtime/Swift/Sources/Antlr4/atn/ParserATNSimulator.swift
@@ -1132,9 +1132,7 @@ open class ParserATNSimulator: ATNSimulator {
         _ altToPred: [SemanticContext?]) -> [DFAState.PredPrediction]? {
             var pairs = [DFAState.PredPrediction]()
             var containsPredicate = false
-            let length = altToPred.count
-            for i in 1..<length {
-                let pred = altToPred[i]
+            for (i, pred) in altToPred.enumerated().dropFirst() {
 
                 // unpredicated is indicated by SemanticContext.NONE
                 assert(pred != nil, "Expected: pred!=null")
diff --git a/runtime/Swift/Sources/Antlr4/atn/PredictionContext.swift b/runtime/Swift/Sources/Antlr4/atn/PredictionContext.swift
index 0e7026df45..b14c82fa53 100644
--- a/runtime/Swift/Sources/Antlr4/atn/PredictionContext.swift
+++ b/runtime/Swift/Sources/Antlr4/atn/PredictionContext.swift
@@ -123,13 +123,11 @@ public class PredictionContext: Hashable, CustomStringConvertible {
 
     static func calculateHashCode(_ parents: [PredictionContext?], _ returnStates: [Int]) -> Int {
         var hash = MurmurHash.initialize(INITIAL_HASH)
-        var length = parents.count
-        for i in 0..<length {
-            hash = MurmurHash.update(hash, parents[i])
+        for parent in parents {
+            hash = MurmurHash.update(hash, parent)
         }
-        length = returnStates.count
-        for i in 0..<length {
-            hash = MurmurHash.update(hash, returnStates[i])
+        for state in returnStates {
+            hash = MurmurHash.update(hash, state)
         }
 
         return  MurmurHash.finish(hash, 2 * parents.count)