reduce unneeded internal use of IEnumerable<T>

src/SMAPI.Mods.ConsoleCommands/Framework/Commands/ArgumentParser.cs

@@ -111,7 +111,7 @@ internal class ArgumentParser : IReadOnlyList<string>
     /// <returns>An enumerator that can be used to iterate through the collection.</returns>
     public IEnumerator<string> GetEnumerator()
     {
-        return ((IEnumerable<string>)this.Values).GetEnumerator();
+        return ((IReadOnlyList<string>)this.Values).GetEnumerator();
     }
 
     /// <summary>Returns an enumerator that iterates through a collection.</summary>

src/SMAPI.Mods.ConsoleCommands/Framework/Commands/ConsoleCommand.cs

@@ -73,7 +73,7 @@ internal abstract class ConsoleCommand : IConsoleCommand
     /// <param name="data">The data to display.</param>
     /// <param name="header">The table header.</param>
     /// <param name="getRow">Returns a set of fields for a data value.</param>
-    protected string GetTableString<T>(IEnumerable<T> data, string[] header, Func<T, string[]> getRow)
+    protected string GetTableString<T>(T[] data, string[] header, Func<T, string[]> getRow)
     {
         // get table data
         int[] widths = header.Select(p => p.Length).ToArray();

src/SMAPI.Tests/Utilities/KeybindListTests.cs

@@ -121,10 +121,9 @@ internal class KeybindListTests
     ** Private methods
     *********/
     /// <summary>Get all defined buttons.</summary>
-    private static IEnumerable<SButton> GetAllButtons()
+    private static SButton[] GetAllButtons()
     {
-        foreach (SButton button in Enum.GetValues<SButton>())
-            yield return button;
+        return Enum.GetValues<SButton>();
     }
 
     /// <summary>Get the button state defined by a mapping string.</summary>

src/SMAPI.Toolkit/Framework/ModData/ModDataModel.cs

@@ -109,13 +109,17 @@ internal class ModDataModel
     }
 
     /// <summary>Get the former mod IDs.</summary>
-    public IEnumerable<string> GetFormerIds()
+    public string[] GetFormerIds()
     {
-        if (this.FormerIds != null)
-        {
-            foreach (string id in this.FormerIds.Split('|'))
-                yield return id.Trim();
-        }
+#if NET6_0_OR_GREATER
+        return
+            this.FormerIds?.Split('|', StringSplitOptions.TrimEntries)
+            ?? [];
+#else
+        return this.FormerIds != null
+            ? this.FormerIds.Split('|').Select(id => id.Trim()).ToArray()
+            : [];
+#endif
     }
 
 

src/SMAPI.Toolkit/Framework/ModData/ModDataRecord.cs

@@ -39,7 +39,7 @@ public class ModDataRecord
     {
         this.DisplayName = displayName;
         this.ID = model.Id;
-        this.FormerIDs = model.GetFormerIds().ToArray();
+        this.FormerIDs = model.GetFormerIds();
         this.SuppressWarnings = model.SuppressWarnings;
         this.IgnoreDependencies = model.IgnoreDependencies;
         this.Fields = model.GetFields().ToArray();

src/SMAPI.Toolkit/Framework/ModData/ModDatabase.cs

@@ -34,7 +34,7 @@ public class ModDatabase
     }
 
     /// <summary>Get all mod data records.</summary>
-    public IEnumerable<ModDataRecord> GetAll()
+    public IReadOnlyList<ModDataRecord> GetAll()
     {
         return this.Records;
     }

src/SMAPI.Toolkit/Framework/ModScanning/ModFolder.cs

@@ -90,7 +90,7 @@ public class ModFolder
 
     /// <summary>Get the update keys for a mod.</summary>
     /// <param name="manifest">The mod manifest.</param>
-    public IEnumerable<string> GetUpdateKeys(Manifest manifest)
+    public IReadOnlyList<string> GetUpdateKeys(Manifest manifest)
     {
         return
             manifest.UpdateKeys

src/SMAPI/Events/BuildingListChangedEventArgs.cs

@@ -32,7 +32,7 @@ public class BuildingListChangedEventArgs : EventArgs
     /// <param name="location">The location which changed.</param>
     /// <param name="added">The buildings added to the location.</param>
     /// <param name="removed">The buildings removed from the location.</param>
-    internal BuildingListChangedEventArgs(GameLocation location, IEnumerable<Building> added, IEnumerable<Building> removed)
+    internal BuildingListChangedEventArgs(GameLocation location, IReadOnlyList<Building> added, IReadOnlyList<Building> removed)
     {
         this.Location = location;
         this.Added = added.ToArray();

src/SMAPI/Events/DebrisListChangedEventArgs.cs

@@ -31,7 +31,7 @@ public class DebrisListChangedEventArgs : EventArgs
     /// <param name="location">The location which changed.</param>
     /// <param name="added">The debris added to the location.</param>
     /// <param name="removed">The debris removed from the location.</param>
-    internal DebrisListChangedEventArgs(GameLocation location, IEnumerable<Debris> added, IEnumerable<Debris> removed)
+    internal DebrisListChangedEventArgs(GameLocation location, IReadOnlyList<Debris> added, IReadOnlyList<Debris> removed)
     {
         this.Location = location;
         this.Added = added.ToArray();

src/SMAPI/Events/FurnitureListChangedEventArgs.cs

@@ -32,7 +32,7 @@ public class FurnitureListChangedEventArgs : EventArgs
     /// <param name="location">The location which changed.</param>
     /// <param name="added">The furniture added to the location.</param>
     /// <param name="removed">The furniture removed from the location.</param>
-    internal FurnitureListChangedEventArgs(GameLocation location, IEnumerable<Furniture> added, IEnumerable<Furniture> removed)
+    internal FurnitureListChangedEventArgs(GameLocation location, IReadOnlyList<Furniture> added, IReadOnlyList<Furniture> removed)
     {
         this.Location = location;
         this.Added = added.ToArray();

src/SMAPI/Events/LargeTerrainFeatureListChangedEventArgs.cs

@@ -32,7 +32,7 @@ public class LargeTerrainFeatureListChangedEventArgs : EventArgs
     /// <param name="location">The location which changed.</param>
     /// <param name="added">The large terrain features added to the location.</param>
     /// <param name="removed">The large terrain features removed from the location.</param>
-    internal LargeTerrainFeatureListChangedEventArgs(GameLocation location, IEnumerable<LargeTerrainFeature> added, IEnumerable<LargeTerrainFeature> removed)
+    internal LargeTerrainFeatureListChangedEventArgs(GameLocation location, IReadOnlyList<LargeTerrainFeature> added, IReadOnlyList<LargeTerrainFeature> removed)
     {
         this.Location = location;
         this.Added = added.ToArray();

src/SMAPI/Events/LocationListChangedEventArgs.cs

@@ -24,7 +24,7 @@ public class LocationListChangedEventArgs : EventArgs
     /// <summary>Construct an instance.</summary>
     /// <param name="added">The added locations.</param>
     /// <param name="removed">The removed locations.</param>
-    internal LocationListChangedEventArgs(IEnumerable<GameLocation> added, IEnumerable<GameLocation> removed)
+    internal LocationListChangedEventArgs(IReadOnlyList<GameLocation> added, IReadOnlyList<GameLocation> removed)
     {
         this.Added = added.ToArray();
         this.Removed = removed.ToArray();

src/SMAPI/Events/NpcListChangedEventArgs.cs

@@ -31,7 +31,7 @@ public class NpcListChangedEventArgs : EventArgs
     /// <param name="location">The location which changed.</param>
     /// <param name="added">The NPCs added to the location.</param>
     /// <param name="removed">The NPCs removed from the location.</param>
-    internal NpcListChangedEventArgs(GameLocation location, IEnumerable<NPC> added, IEnumerable<NPC> removed)
+    internal NpcListChangedEventArgs(GameLocation location, IReadOnlyList<NPC> added, IReadOnlyList<NPC> removed)
     {
         this.Location = location;
         this.Added = added.ToArray();

src/SMAPI/Events/ObjectListChangedEventArgs.cs

@@ -33,7 +33,7 @@ public class ObjectListChangedEventArgs : EventArgs
     /// <param name="location">The location which changed.</param>
     /// <param name="added">The objects added to the location.</param>
     /// <param name="removed">The objects removed from the location.</param>
-    internal ObjectListChangedEventArgs(GameLocation location, IEnumerable<KeyValuePair<Vector2, Object>> added, IEnumerable<KeyValuePair<Vector2, Object>> removed)
+    internal ObjectListChangedEventArgs(GameLocation location, IReadOnlyList<KeyValuePair<Vector2, Object>> added, IReadOnlyList<KeyValuePair<Vector2, Object>> removed)
     {
         this.Location = location;
         this.Added = added.ToArray();

src/SMAPI/Events/TerrainFeatureListChangedEventArgs.cs

@@ -33,7 +33,7 @@ public class TerrainFeatureListChangedEventArgs : EventArgs
     /// <param name="location">The location which changed.</param>
     /// <param name="added">The terrain features added to the location.</param>
     /// <param name="removed">The terrain features removed from the location.</param>
-    internal TerrainFeatureListChangedEventArgs(GameLocation location, IEnumerable<KeyValuePair<Vector2, TerrainFeature>> added, IEnumerable<KeyValuePair<Vector2, TerrainFeature>> removed)
+    internal TerrainFeatureListChangedEventArgs(GameLocation location, IReadOnlyList<KeyValuePair<Vector2, TerrainFeature>> added, IReadOnlyList<KeyValuePair<Vector2, TerrainFeature>> removed)
     {
         this.Location = location;
         this.Added = added.ToArray();

src/SMAPI/Framework/ContentCoordinator.cs

@@ -463,7 +463,7 @@ internal class ContentCoordinator : IDisposable
                 ICollection<IAssetName> invalidatedKeys = invalidatedAssets.Keys;
                 IAssetName[] propagatedKeys = propagated.Where(p => p.Value).Select(p => p.Key).ToArray();
 
-                string FormatKeyList(IEnumerable<IAssetName> keys) => string.Join(", ", keys.Select(p => p.Name).OrderBy(p => p, StringComparer.OrdinalIgnoreCase));
+                string FormatKeyList(ICollection<IAssetName> keys) => string.Join(", ", keys.Select(p => p.Name).OrderBy(p => p, StringComparer.OrdinalIgnoreCase));
 
                 report.AppendLine($"Invalidated {invalidatedKeys.Count} asset names ({FormatKeyList(invalidatedKeys)}).");
                 report.AppendLine(propagated.Count > 0
@@ -494,7 +494,7 @@ internal class ContentCoordinator : IDisposable
     /// <summary>Get all loaded instances of an asset name.</summary>
     /// <param name="assetName">The asset name.</param>
     [SuppressMessage("ReSharper", "UnusedMember.Global", Justification = "This method is provided for Content Patcher.")]
-    public IEnumerable<object> GetLoadedValues(IAssetName assetName)
+    public IReadOnlyList<object> GetLoadedValues(IAssetName assetName)
     {
         return this.ContentManagerLock.InReadLock(() =>
         {
@@ -596,7 +596,7 @@ internal class ContentCoordinator : IDisposable
 
     /// <summary>Get the language enums (like <see cref="LocalizedContentManager.LanguageCode.ja"/>) indexed by locale code (like <c>ja-JP</c>).</summary>
     /// <param name="customLanguages">The custom languages to add to the lookup.</param>
-    private Dictionary<string, LocalizedContentManager.LanguageCode> GetLocaleCodes(IEnumerable<ModLanguage?> customLanguages)
+    private Dictionary<string, LocalizedContentManager.LanguageCode> GetLocaleCodes(IReadOnlyList<ModLanguage?> customLanguages)
     {
         var map = new Dictionary<string, LocalizedContentManager.LanguageCode>(StringComparer.OrdinalIgnoreCase);
 

src/SMAPI/Framework/Logging/LogManager.cs

@@ -388,7 +388,7 @@ internal class LogManager : IDisposable
     /// <param name="logTechnicalDetailsForBrokenMods">Whether to include more technical details about broken mods in the TRACE logs. This is mainly useful for creating compatibility rewriters.</param>
     /// <param name="hasHarmonyFix">Whether Harmony was fixed to work with Stardew Valley.</param>
     [SuppressMessage("ReSharper", "ConditionalAccessQualifierIsNonNullableAccordingToAPIContract", Justification = "Manifests aren't guaranteed non-null at this point in the loading process.")]
-    private void LogModWarnings(IEnumerable<IModMetadata> mods, IReadOnlyList<IModMetadata> skippedMods, bool logParanoidWarnings, bool logTechnicalDetailsForBrokenMods, bool hasHarmonyFix)
+    private void LogModWarnings(IReadOnlyList<IModMetadata> mods, IReadOnlyList<IModMetadata> skippedMods, bool logParanoidWarnings, bool logTechnicalDetailsForBrokenMods, bool hasHarmonyFix)
     {
         // get mods with warnings
         IModMetadata[] modsWithWarnings = mods
@@ -526,7 +526,7 @@ internal class LogManager : IDisposable
 
     /// <summary>Group failed mods by the priority players should update them, where mods in earlier groups are more likely to fix multiple mods.</summary>
     /// <param name="failedMods">The failed mods to group.</param>
-    private IEnumerable<IList<IModMetadata>> GroupFailedModsByPriority(IReadOnlyList<IModMetadata> failedMods)
+    private IReadOnlyList<IModMetadata>[] GroupFailedModsByPriority(IReadOnlyList<IModMetadata> failedMods)
     {
         var failedOthers = failedMods.ToList();
         var skippedModIds = new HashSet<string>(from mod in failedMods where mod.HasId() select mod.Manifest.UniqueID, StringComparer.OrdinalIgnoreCase);

src/SMAPI/Framework/ModHelpers/DataHelper.cs

@@ -150,14 +150,14 @@ internal class DataHelper : BaseHelper, IDataHelper
 
     /// <summary>Get the data fields to read/write for save data.</summary>
     /// <param name="stage">The current load stage.</param>
-    private IEnumerable<IDictionary<string, string>> GetDataFields(LoadStage stage)
+    private IDictionary<string, string>[] GetDataFields(LoadStage stage)
     {
         if (stage == LoadStage.None)
-            yield break;
+            return [];
 
-        yield return Game1.CustomData;
-        if (SaveGame.loaded != null)
-            yield return SaveGame.loaded.CustomData;
+        return SaveGame.loaded != null
+            ? [Game1.CustomData, SaveGame.loaded.CustomData]
+            : [Game1.CustomData];
     }
 
     /// <summary>Get the absolute path for a global data file.</summary>

src/SMAPI/Framework/SMultiplayer.cs

@@ -508,16 +508,27 @@ internal class SMultiplayer : Multiplayer
         }
 
         // get player IDs
-        HashSet<long> playerIds = new(model.ToPlayerIds ?? this.GetKnownPlayerIds());
+        bool sendToSelf;
+        ICollection<long> peerIds;
+        if (model.ToPlayerIds != null)
+        {
+            peerIds = new HashSet<long>(model.ToPlayerIds);
+            sendToSelf = peerIds.Contains(Game1.player.UniqueMultiplayerID);
+        }
+        else
+        {
+            peerIds = this.Peers.Keys;
+            sendToSelf = true;
+        }
 
         // notify local mods
-        if (playerIds.Contains(Game1.player.UniqueMultiplayerID))
+        if (sendToSelf)
             this.OnModMessageReceived(model);
 
         // forward to other players
-        if (Context.IsMainPlayer && playerIds.Any(p => p != Game1.player.UniqueMultiplayerID))
+        if (Context.IsMainPlayer)
         {
-            foreach (long playerId in playerIds)
+            foreach (long playerId in peerIds)
             {
                 if (playerId != Game1.player.UniqueMultiplayerID && playerId != model.FromPlayerId && this.Peers.TryGetValue(playerId, out MultiplayerPeer? peer))
                 {
@@ -540,14 +551,6 @@ internal class SMultiplayer : Multiplayer
         return SGameRunner.Instance.GetScreenId(playerId);
     }
 
-    /// <summary>Get all connected player IDs, including the current player.</summary>
-    private IEnumerable<long> GetKnownPlayerIds()
-    {
-        yield return Game1.player.UniqueMultiplayerID;
-        foreach (long peerId in this.Peers.Keys)
-            yield return peerId;
-    }
-
     /// <summary>Get the fields to include in a context sync message sent to other players.</summary>
     private object[] GetContextSyncMessageFields()
     {

src/SMAPI/Framework/SnapshotListDiff.cs

@@ -37,7 +37,7 @@ internal class SnapshotListDiff<T>
     /// <param name="isChanged">Whether the value changed since the last update.</param>
     /// <param name="removed">The removed values.</param>
     /// <param name="added">The added values.</param>
-    public void Update(bool isChanged, IEnumerable<T>? removed, IEnumerable<T>? added)
+    public void Update(bool isChanged, IReadOnlyCollection<T>? removed, IReadOnlyCollection<T>? added)
     {
         this.IsChanged = isChanged;
 

src/SMAPI/Framework/StateTracking/FieldWatchers/ComparableListWatcher.cs

@@ -36,10 +36,10 @@ internal class ComparableListWatcher<TValue> : BaseDisposableWatcher, ICollectio
     public bool IsChanged => this.AddedImpl.Count > 0 || this.RemovedImpl.Count > 0;
 
     /// <inheritdoc />
-    public IEnumerable<TValue> Added => this.AddedImpl;
+    public IReadOnlyCollection<TValue> Added => this.AddedImpl;
 
     /// <inheritdoc />
-    public IEnumerable<TValue> Removed => this.RemovedImpl;
+    public IReadOnlyCollection<TValue> Removed => this.RemovedImpl;
 
 
     /*********

src/SMAPI/Framework/StateTracking/FieldWatchers/ImmutableCollectionWatcher.cs

@@ -20,10 +20,10 @@ internal class ImmutableCollectionWatcher<TValue> : BaseDisposableWatcher, IColl
     public bool IsChanged { get; } = false;
 
     /// <inheritdoc />
-    public IEnumerable<TValue> Added { get; } = [];
+    public IReadOnlyCollection<TValue> Added { get; } = [];
 
     /// <inheritdoc />
-    public IEnumerable<TValue> Removed { get; } = [];
+    public IReadOnlyCollection<TValue> Removed { get; } = [];
 
 
     /*********

src/SMAPI/Framework/StateTracking/FieldWatchers/InventoryWatcher.cs

@@ -38,10 +38,10 @@ internal class InventoryWatcher : BaseDisposableWatcher, ICollectionWatcher<Item
     public bool IsChanged => this.AddedImpl.Count > 0 || this.RemovedImpl.Count > 0;
 
     /// <inheritdoc />
-    public IEnumerable<Item> Added => this.AddedImpl;
+    public IReadOnlyCollection<Item> Added => this.AddedImpl;
 
     /// <inheritdoc />
-    public IEnumerable<Item> Removed => this.RemovedImpl;
+    public IReadOnlyCollection<Item> Removed => this.RemovedImpl;
 
 
     /*********

src/SMAPI/Framework/StateTracking/FieldWatchers/NetCollectionWatcher.cs

@@ -31,10 +31,10 @@ internal class NetCollectionWatcher<TValue> : BaseDisposableWatcher, ICollection
     public bool IsChanged => this.AddedImpl.Count > 0 || this.RemovedImpl.Count > 0;
 
     /// <inheritdoc />
-    public IEnumerable<TValue> Added => this.AddedImpl;
+    public IReadOnlyCollection<TValue> Added => this.AddedImpl;
 
     /// <inheritdoc />
-    public IEnumerable<TValue> Removed => this.RemovedImpl;
+    public IReadOnlyCollection<TValue> Removed => this.RemovedImpl;
 
 
     /*********

src/SMAPI/Framework/StateTracking/FieldWatchers/NetDictionaryWatcher.cs

@@ -19,10 +19,10 @@ internal class NetDictionaryWatcher<TKey, TValue, TField, TSerialDict, TSelf> :
     ** Fields
     *********/
     /// <summary>The pairs added since the last reset.</summary>
-    private readonly IDictionary<TKey, TValue> PairsAdded = new Dictionary<TKey, TValue>();
+    private readonly Dictionary<TKey, TValue> PairsAdded = [];
 
     /// <summary>The pairs removed since the last reset.</summary>
-    private readonly IDictionary<TKey, TValue> PairsRemoved = new Dictionary<TKey, TValue>();
+    private readonly Dictionary<TKey, TValue> PairsRemoved = [];
 
     /// <summary>The field being watched.</summary>
     private readonly NetDictionary<TKey, TValue, TField, TSerialDict, TSelf> Field;
@@ -38,10 +38,10 @@ internal class NetDictionaryWatcher<TKey, TValue, TField, TSerialDict, TSelf> :
     public bool IsChanged => this.PairsAdded.Count > 0 || this.PairsRemoved.Count > 0;
 
     /// <inheritdoc />
-    public IEnumerable<KeyValuePair<TKey, TValue>> Added => this.PairsAdded;
+    public IReadOnlyCollection<KeyValuePair<TKey, TValue>> Added => this.PairsAdded;
 
     /// <inheritdoc />
-    public IEnumerable<KeyValuePair<TKey, TValue>> Removed => this.PairsRemoved;
+    public IReadOnlyCollection<KeyValuePair<TKey, TValue>> Removed => this.PairsRemoved;
 
 
     /*********

src/SMAPI/Framework/StateTracking/FieldWatchers/ObservableCollectionWatcher.cs

@@ -34,10 +34,10 @@ internal class ObservableCollectionWatcher<TValue> : BaseDisposableWatcher, ICol
     public bool IsChanged => this.AddedImpl.Count > 0 || this.RemovedImpl.Count > 0;
 
     /// <inheritdoc />
-    public IEnumerable<TValue> Added => this.AddedImpl;
+    public IReadOnlyCollection<TValue> Added => this.AddedImpl;
 
     /// <inheritdoc />
-    public IEnumerable<TValue> Removed => this.RemovedImpl;
+    public IReadOnlyCollection<TValue> Removed => this.RemovedImpl;
 
 
     /*********

src/SMAPI/Framework/StateTracking/ICollectionWatcher.cs

@@ -9,8 +9,8 @@ internal interface ICollectionWatcher<out TValue> : IWatcher
     ** Accessors
     *********/
     /// <summary>The values added since the last reset.</summary>
-    IEnumerable<TValue> Added { get; }
+    IReadOnlyCollection<TValue> Added { get; }
 
     /// <summary>The values removed since the last reset.</summary>
-    IEnumerable<TValue> Removed { get; }
+    IReadOnlyCollection<TValue> Removed { get; }
 }

src/SMAPI/Framework/StateTracking/Snapshots/WorldLocationsSnapshot.cs

@@ -24,7 +24,7 @@ internal class WorldLocationsSnapshot
     public SnapshotListDiff<GameLocation> LocationList { get; } = new();
 
     /// <summary>The tracked locations.</summary>
-    public IEnumerable<LocationSnapshot> Locations => this.LocationsDict.Values;
+    public IReadOnlyCollection<LocationSnapshot> Locations => this.LocationsDict.Values;
 
 
     /*********

src/SMAPI/Framework/StateTracking/WorldLocationsTracker.cs

@@ -29,6 +29,12 @@ internal class WorldLocationsTracker : IWatcher
     /// <summary>A lookup of registered buildings and their indoor location.</summary>
     private readonly Dictionary<Building, GameLocation?> BuildingIndoors = new(new ObjectReferenceComparer<Building>());
 
+    /// <summary>The backing field for <see cref="Added"/>.</summary>
+    private readonly HashSet<GameLocation> AddedImpl = new(new ObjectReferenceComparer<GameLocation>());
+
+    /// <summary>The backing field for <see cref="Removed"/>.</summary>
+    private readonly HashSet<GameLocation> RemovedImpl = new(new ObjectReferenceComparer<GameLocation>());
+
     /// <summary>The pooled list instance for <see cref="GetLocationsWhoseBuildingsChanged"/>.</summary>
     private static readonly List<LocationTracker> PooledLocationsWithBuildingsChanged = [];
 
@@ -49,13 +55,13 @@ internal class WorldLocationsTracker : IWatcher
     public bool IsChanged => this.IsLocationListChanged || this.LocationsHaveChanges;
 
     /// <summary>The tracked locations.</summary>
-    public IEnumerable<LocationTracker> Locations => this.LocationDict.Values;
-
-    /// <summary>The locations removed since the last update.</summary>
-    public ICollection<GameLocation> Added { get; } = new HashSet<GameLocation>(new ObjectReferenceComparer<GameLocation>());
+    public IReadOnlyCollection<LocationTracker> Locations => this.LocationDict.Values;
 
     /// <summary>The locations added since the last update.</summary>
-    public ICollection<GameLocation> Removed { get; } = new HashSet<GameLocation>(new ObjectReferenceComparer<GameLocation>());
+    public IReadOnlySet<GameLocation> Added => this.AddedImpl;
+
+    /// <summary>The locations removed since the last update.</summary>
+    public IReadOnlySet<GameLocation> Removed => this.RemovedImpl;
 
 
     /*********
@@ -130,8 +136,9 @@ internal class WorldLocationsTracker : IWatcher
     /// <summary>Set the current location list as the baseline.</summary>
     public void ResetLocationList()
     {
-        this.Removed.Clear();
-        this.Added.Clear();
+        this.RemovedImpl.Clear();
+        this.AddedImpl.Clear();
+
         this.LocationListWatcher.Reset();
         this.MineLocationListWatcher.Reset();
         this.VolcanoLocationListWatcher.Reset();
@@ -143,7 +150,8 @@ internal class WorldLocationsTracker : IWatcher
         this.LocationsHaveChanges = false;
 
         this.ResetLocationList();
-        foreach (IWatcher watcher in this.GetWatchers())
+
+        foreach (LocationTracker watcher in this.Locations)
             watcher.Reset();
     }
 
@@ -157,7 +165,11 @@ internal class WorldLocationsTracker : IWatcher
     /// <inheritdoc />
     public void Dispose()
     {
-        foreach (IWatcher watcher in this.GetWatchers())
+        this.LocationListWatcher.Dispose();
+        this.MineLocationListWatcher.Dispose();
+        this.VolcanoLocationListWatcher.Dispose();
+
+        foreach (LocationTracker watcher in this.Locations)
             watcher.Dispose();
     }
 
@@ -226,7 +238,7 @@ internal class WorldLocationsTracker : IWatcher
         this.Remove(location);
 
         // add location
-        this.Added.Add(location);
+        this.AddedImpl.Add(location);
         this.LocationDict[location] = new LocationTracker(location);
 
         // add buildings
@@ -254,7 +266,7 @@ internal class WorldLocationsTracker : IWatcher
         if (this.LocationDict.TryGetValue(location, out LocationTracker? watcher))
         {
             // track change
-            this.Removed.Add(location);
+            this.RemovedImpl.Add(location);
 
             // remove
             this.LocationDict.Remove(location);
@@ -266,16 +278,6 @@ internal class WorldLocationsTracker : IWatcher
     /****
     ** Helpers
     ****/
-    /// <summary>The underlying watchers.</summary>
-    private IEnumerable<IWatcher> GetWatchers()
-    {
-        yield return this.LocationListWatcher;
-        yield return this.MineLocationListWatcher;
-        yield return this.VolcanoLocationListWatcher;
-        foreach (LocationTracker watcher in this.Locations)
-            yield return watcher;
-    }
-
     /// <summary>Get the locations whose building list changed, if any.</summary>
     private List<LocationTracker> GetLocationsWhoseBuildingsChanged()
     {

src/SMAPI/Framework/Translator.cs

@@ -70,7 +70,7 @@ internal class Translator
     }
 
     /// <summary>Get all translations for the current locale.</summary>
-    public IEnumerable<Translation> GetTranslations()
+    public IReadOnlyList<Translation> GetTranslations()
     {
         return this.ForLocale.Values.ToArray();
     }
@@ -130,7 +130,7 @@ internal class Translator
     ** Private methods
     *********/
     /// <summary>Get all translation keys in the underlying translation data, ignoring the <see cref="ForLocale"/> cache.</summary>
-    private IEnumerable<string> GetAllKeysRaw()
+    private HashSet<string> GetAllKeysRaw()
     {
         return new HashSet<string>(
             this.All.SelectMany(p => p.Value.Keys),

src/SMAPI/Metadata/CoreAssetPropagator.cs

@@ -746,7 +746,7 @@ internal class CoreAssetPropagator
     ** Helpers
     ****/
     /// <summary>Get all NPCs in the game (excluding farm animals).</summary>
-    private IEnumerable<NPC> GetCharacters()
+    private IReadOnlyList<NPC> GetCharacters()
     {
         return this.WorldCache.GetOrSet(
             nameof(this.GetCharacters),
@@ -772,7 +772,7 @@ internal class CoreAssetPropagator
     }
 
     /// <summary>Get all farm animals in the game.</summary>
-    private IEnumerable<FarmAnimal> GetFarmAnimals()
+    private IReadOnlyList<FarmAnimal> GetFarmAnimals()
     {
         return this.WorldCache.GetOrSet(
             nameof(this.GetFarmAnimals),
@@ -796,7 +796,7 @@ internal class CoreAssetPropagator
 
     /// <summary>Get all locations in the game.</summary>
     /// <param name="buildingInteriors">Whether to also get the interior locations for constructable buildings.</param>
-    private IEnumerable<GameLocation> GetLocations(bool buildingInteriors = true)
+    private IReadOnlyList<GameLocation> GetLocations(bool buildingInteriors = true)
     {
         return this.WorldCache.GetOrSet(
             $"{nameof(this.GetLocations)}_{buildingInteriors}",
@@ -806,7 +806,7 @@ internal class CoreAssetPropagator
 
     /// <summary>Get all locations in the game.</summary>
     /// <param name="buildingInteriors">Whether to also get the interior locations for constructable buildings.</param>
-    private IEnumerable<LocationInfo> GetLocationsWithInfo(bool buildingInteriors = true)
+    private IReadOnlyList<LocationInfo> GetLocationsWithInfo(bool buildingInteriors = true)
     {
         return this.WorldCache.GetOrSet(
             $"{nameof(this.GetLocationsWithInfo)}_{buildingInteriors}",