diff --git a/Dapper.SqlBuilder/SqlBuilder.cs b/Dapper.SqlBuilder/SqlBuilder.cs
index 5726fdc6e..cb45d0582 100644
--- a/Dapper.SqlBuilder/SqlBuilder.cs
+++ b/Dapper.SqlBuilder/SqlBuilder.cs
@@ -10,7 +10,7 @@ public class SqlBuilder
         private readonly Dictionary<string, Clauses> _data = new Dictionary<string, Clauses>();
         private int _seq;
 
-        private class Clause
+        private sealed class Clause
         {
             public Clause(string sql, object? parameters, bool isInclusive)
             {
@@ -23,7 +23,7 @@ public Clause(string sql, object? parameters, bool isInclusive)
             public bool IsInclusive { get; }
         }
 
-        private class Clauses : List<Clause>
+        private sealed class Clauses : List<Clause>
         {
             private readonly string _joiner, _prefix, _postfix;
 
@@ -36,11 +36,9 @@ public Clauses(string joiner, string prefix = "", string postfix = "")
 
             public string ResolveClauses(DynamicParameters p)
             {
-                foreach (var item in this)
-                {
-                    p.AddDynamicParams(item.Parameters);
-                }
-                return this.Any(a => a.IsInclusive)
+                ForEach(item => p.AddDynamicParams(item.Parameters));
+
+                return Exists(a => a.IsInclusive)
                     ? _prefix +
                       string.Join(_joiner,
                           this.Where(a => !a.IsInclusive)
diff --git a/Dapper/DefaultTypeMap.cs b/Dapper/DefaultTypeMap.cs
index 98029741a..c2f691883 100644
--- a/Dapper/DefaultTypeMap.cs
+++ b/Dapper/DefaultTypeMap.cs
@@ -10,7 +10,7 @@ namespace Dapper
     /// </summary>
     public sealed class DefaultTypeMap : SqlMapper.ITypeMap
     {
-        private readonly List<FieldInfo> _fields;
+        private readonly FieldInfo[] _fields;
         private readonly Type _type;
 
         /// <summary>
@@ -42,7 +42,7 @@ internal static MethodInfo GetPropertySetterOrThrow(PropertyInfo propertyInfo, T
                    BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance,
                    Type.DefaultBinder,
                    propertyInfo.PropertyType,
-                   propertyInfo.GetIndexParameters().Select(p => p.ParameterType).ToArray(),
+                   Array.ConvertAll(propertyInfo.GetIndexParameters(), p => p.ParameterType),
                    null)!.GetSetMethod(true);
         }
 
@@ -54,9 +54,9 @@ internal static List<PropertyInfo> GetSettableProps(Type t)
                   .ToList();
         }
 
-        internal static List<FieldInfo> GetSettableFields(Type t)
+        private static FieldInfo[] GetSettableFields(Type t)
         {
-            return t.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance).ToList();
+            return t.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
         }
 
         /// <summary>
@@ -156,20 +156,20 @@ public SqlMapper.IMemberMap GetConstructorParameter(ConstructorInfo constructor,
 
             // preference order is:
             // exact match over underscore match, exact case over wrong case, backing fields over regular fields, match-inc-underscores over match-exc-underscores
-            var field = _fields.Find(p => string.Equals(p.Name, columnName, StringComparison.Ordinal))
-                ?? _fields.Find(p => string.Equals(p.Name, backingFieldName, StringComparison.Ordinal))
-                ?? _fields.Find(p => string.Equals(p.Name, columnName, StringComparison.OrdinalIgnoreCase))
-                ?? _fields.Find(p => string.Equals(p.Name, backingFieldName, StringComparison.OrdinalIgnoreCase));
+            var field = Array.Find(_fields, p => string.Equals(p.Name, columnName, StringComparison.Ordinal))
+                ?? Array.Find(_fields, p => string.Equals(p.Name, backingFieldName, StringComparison.Ordinal))
+                ?? Array.Find(_fields, p => string.Equals(p.Name, columnName, StringComparison.OrdinalIgnoreCase))
+                ?? Array.Find(_fields, p => string.Equals(p.Name, backingFieldName, StringComparison.OrdinalIgnoreCase));
 
             if (field is null && MatchNamesWithUnderscores)
             {
                 var effectiveColumnName = columnName.Replace("_", "");
                 backingFieldName = "<" + effectiveColumnName + ">k__BackingField";
 
-                field = _fields.Find(p => string.Equals(p.Name, effectiveColumnName, StringComparison.Ordinal))
-                    ?? _fields.Find(p => string.Equals(p.Name, backingFieldName, StringComparison.Ordinal))
-                    ?? _fields.Find(p => string.Equals(p.Name, effectiveColumnName, StringComparison.OrdinalIgnoreCase))
-                    ?? _fields.Find(p => string.Equals(p.Name, backingFieldName, StringComparison.OrdinalIgnoreCase));
+                field = Array.Find(_fields, p => string.Equals(p.Name, effectiveColumnName, StringComparison.Ordinal))
+                    ?? Array.Find(_fields, p => string.Equals(p.Name, backingFieldName, StringComparison.Ordinal))
+                    ?? Array.Find(_fields, p => string.Equals(p.Name, effectiveColumnName, StringComparison.OrdinalIgnoreCase))
+                    ?? Array.Find(_fields, p => string.Equals(p.Name, backingFieldName, StringComparison.OrdinalIgnoreCase));
             }
 
             if (field is not null)
diff --git a/Dapper/DynamicParameters.cs b/Dapper/DynamicParameters.cs
index f6708b5ce..1feb4d020 100644
--- a/Dapper/DynamicParameters.cs
+++ b/Dapper/DynamicParameters.cs
@@ -62,10 +62,7 @@ public void AddDynamicParams(object? param)
                     if (subDynamic.templates is not null)
                     {
                         templates ??= new List<object>();
-                        foreach (var t in subDynamic.templates)
-                        {
-                            templates.Add(t);
-                        }
+                        templates.AddRange(subDynamic.templates);
                     }
                 }
                 else
@@ -212,14 +209,7 @@ protected void AddParameters(IDbCommand command, SqlMapper.Identity identity)
                 }
 
                 // Now that the parameters are added to the command, let's place our output callbacks
-                var tmp = outputCallbacks;
-                if (tmp is not null)
-                {
-                    foreach (var generator in tmp)
-                    {
-                        generator();
-                    }
-                }
+                outputCallbacks?.ForEach(generator => generator());
             }
 
             foreach (var param in parameters.Values)
diff --git a/Dapper/FeatureSupport.cs b/Dapper/FeatureSupport.cs
index 4d7d77e2e..f00c38ed3 100644
--- a/Dapper/FeatureSupport.cs
+++ b/Dapper/FeatureSupport.cs
@@ -6,7 +6,7 @@ namespace Dapper
     /// <summary>
     /// Handles variances in features per DBMS
     /// </summary>
-    internal class FeatureSupport
+    internal sealed class FeatureSupport
     {
         private static readonly FeatureSupport
             Default = new FeatureSupport(false),
diff --git a/Dapper/SqlMapper.CacheInfo.cs b/Dapper/SqlMapper.CacheInfo.cs
index d235beb6f..69edc4eea 100644
--- a/Dapper/SqlMapper.CacheInfo.cs
+++ b/Dapper/SqlMapper.CacheInfo.cs
@@ -7,7 +7,7 @@ namespace Dapper
 {
     public static partial class SqlMapper
     {
-        private class CacheInfo
+        private sealed class CacheInfo
         {
             public DeserializerState Deserializer { get; set; }
             public Func<DbDataReader, object>[]? OtherDeserializers { get; set; }
diff --git a/Dapper/SqlMapper.DontMap.cs b/Dapper/SqlMapper.DontMap.cs
index a97c5811e..765c7b937 100644
--- a/Dapper/SqlMapper.DontMap.cs
+++ b/Dapper/SqlMapper.DontMap.cs
@@ -5,6 +5,6 @@ public static partial class SqlMapper
         /// <summary>
         /// Dummy type for excluding from multi-map
         /// </summary>
-        private class DontMap { /* hiding constructor */ }
+        private sealed class DontMap { /* hiding constructor */ }
     }
 }
diff --git a/Dapper/SqlMapper.Link.cs b/Dapper/SqlMapper.Link.cs
index 92b434881..710714412 100644
--- a/Dapper/SqlMapper.Link.cs
+++ b/Dapper/SqlMapper.Link.cs
@@ -12,7 +12,7 @@ public static partial class SqlMapper
         /// </summary>
         /// <typeparam name="TKey">The type to cache.</typeparam>
         /// <typeparam name="TValue">The value type of the cache.</typeparam>
-        internal class Link<TKey, TValue> where TKey : class
+        internal sealed class Link<TKey, TValue> where TKey : class
         {
             public static void Clear(ref Link<TKey, TValue>? head) => Interlocked.Exchange(ref head, null);
             public static bool TryGet(Link<TKey, TValue>? link, TKey key, [NotNullWhen(true)] out TValue? value)
diff --git a/Dapper/SqlMapper.TypeDeserializerCache.cs b/Dapper/SqlMapper.TypeDeserializerCache.cs
index 2c2f646db..3a34cd292 100644
--- a/Dapper/SqlMapper.TypeDeserializerCache.cs
+++ b/Dapper/SqlMapper.TypeDeserializerCache.cs
@@ -8,7 +8,7 @@ namespace Dapper
 {
     public static partial class SqlMapper
     {
-        private class TypeDeserializerCache
+        private sealed class TypeDeserializerCache
         {
             private TypeDeserializerCache(Type type)
             {
diff --git a/Dapper/SqlMapper.cs b/Dapper/SqlMapper.cs
index d23e949a5..a7f2066d8 100644
--- a/Dapper/SqlMapper.cs
+++ b/Dapper/SqlMapper.cs
@@ -29,7 +29,7 @@ namespace Dapper
     /// </summary>
     public static partial class SqlMapper
     {
-        private class PropertyInfoByNameComparer : IComparer<PropertyInfo>
+        private sealed class PropertyInfoByNameComparer : IComparer<PropertyInfo>
         {
             public int Compare(PropertyInfo? x, PropertyInfo? y) => string.CompareOrdinal(x?.Name, y?.Name);
         }
@@ -3530,9 +3530,9 @@ private static void GenerateDeserializerFromMap(Type type, DbDataReader reader,
                 il.Emit(OpCodes.Ldloc, returnValueLocal); // [target]
             }
 
-            var members = (specializedConstructor is not null
-                ? names.Select(n => typeMap.GetConstructorParameter(specializedConstructor, n))
-                : names.Select(n => typeMap.GetMember(n))).ToList();
+            var members = Array.ConvertAll<string, IMemberMap?>(names, specializedConstructor is not null
+                ? n => typeMap.GetConstructorParameter(specializedConstructor, n)
+                : n => typeMap.GetMember(n));
 
             // stack is now [target]
             bool first = true;
diff --git a/benchmarks/Dapper.Tests.Performance/Massive/Massive.cs b/benchmarks/Dapper.Tests.Performance/Massive/Massive.cs
index f452a95cb..f4c1c8192 100644
--- a/benchmarks/Dapper.Tests.Performance/Massive/Massive.cs
+++ b/benchmarks/Dapper.Tests.Performance/Massive/Massive.cs
@@ -322,7 +322,6 @@ public virtual DbCommand CreateUpdateCommand(object o, object key)
             var settings = (IDictionary<string, object>)expando;
             var sbKeys = new StringBuilder();
             const string stub = "UPDATE {0} SET {1} WHERE {2} = @{3}";
-            var args = new List<object>();
             var result = CreateCommand(stub, null);
             int counter = 0;
             foreach (var item in settings)
diff --git a/benchmarks/Dapper.Tests.Performance/PetaPoco/PetaPoco.cs b/benchmarks/Dapper.Tests.Performance/PetaPoco/PetaPoco.cs
index add3df772..2ffa3887c 100644
--- a/benchmarks/Dapper.Tests.Performance/PetaPoco/PetaPoco.cs
+++ b/benchmarks/Dapper.Tests.Performance/PetaPoco/PetaPoco.cs
@@ -1020,10 +1020,9 @@ public string LastCommand
         {
             get
             {
-                var sb = new StringBuilder();
                 if (_lastSql == null)
                     return "";
-                sb.Append(_lastSql);
+                var sb = new StringBuilder(_lastSql);
                 if (_lastArgs != null)
                 {
                     sb.Append("\r\n\r\n");
@@ -1038,14 +1037,14 @@ public string LastCommand
 
         public static IMapper Mapper { get; set; }
 
-        internal class PocoColumn
+        internal sealed class PocoColumn
         {
             public string ColumnName;
             public PropertyInfo PropertyInfo;
             public bool ResultColumn;
         }
 
-        internal class PocoData
+        internal sealed class PocoData
         {
             public static PocoData ForType(Type t)
             {
@@ -1272,7 +1271,7 @@ public Func<IDataReader, T> GetFactory<T>(string key, bool ForceDateTimesToUtc,
         // ShareableConnection represents either a shared connection used by a transaction,
         // or a one-off connection if not in a transaction.
         // Non-shared connections are disposed 
-        private class ShareableConnection : IDisposable
+        private sealed class ShareableConnection : IDisposable
         {
             public ShareableConnection(Database db)
             {