Make use of delegate variance, so the actual delegate stored is a...

Make use of delegate variance, so the actual delegate stored is a Func<IDataReader, YourType>; this makes it possible to efficiently expose GetRowParser<T> without any extra allocations

Dapper.StrongName/project.json

@@ -5,7 +5,7 @@
   "licenseUrl": "http://www.apache.org/licenses/LICENSE-2.0",
   "summary": "A high performance Micro-ORM",
   "description": "A high performance Micro-ORM supporting SQL Server, MySQL, Sqlite, SqlCE, Firebird etc..",
-  "version": "1.50-beta6",
+  "version": "1.50-beta7",
   "title": "Dapper dot net (strong named)",
   "tags": [ "orm", "sql", "micro-orm" ],
   "copyright": "2015 Stack Exchange, Inc.",

Dapper.Tests/Tests.IDataReader.cs

@@ -14,6 +14,10 @@ public void GetSameReaderForSameShape()
             var origReader = connection.ExecuteReader("select 'abc' as Name, 123 as Id");
             var origParser = origReader.GetRowParser(typeof(HazNameId));
 
+            var typedParser = origReader.GetRowParser<HazNameId>();
+
+            ReferenceEquals(origParser, typedParser).IsEqualTo(true);
+
             var list = origReader.Parse<HazNameId>().ToList();
             list.Count.IsEqualTo(1);
             list[0].Name.IsEqualTo("abc");
@@ -47,8 +51,8 @@ union all
             {
                 if (reader.Read())
                 {
-                    var toFoo = reader.GetRowParser(typeof(Discriminated_Foo));
-                    var toBar = reader.GetRowParser(typeof(Discriminated_Bar));
+                    var toFoo = reader.GetRowParser<Discriminated_BaseType>(typeof(Discriminated_Foo));
+                    var toBar = reader.GetRowParser<Discriminated_BaseType>(typeof(Discriminated_Bar));
 
                     var col = reader.GetOrdinal("Type");
                     do
@@ -56,10 +60,10 @@ union all
                         switch (reader.GetInt32(col))
                         {
                             case 1:
-                                result.Add((Discriminated_BaseType)toFoo(reader));
+                                result.Add(toFoo(reader));
                                 break;
                             case 2:
-                                result.Add((Discriminated_BaseType)toBar(reader));
+                                result.Add(toBar(reader));
                                 break;
                         }
                     } while (reader.Read());

Dapper/SqlMapper.IDataReader.cs

@@ -49,5 +49,19 @@ public static IEnumerable<dynamic> Parse(this IDataReader reader)
         {
             return GetDeserializer(type, reader, startIndex, length, returnNullIfFirstMissing);
         }
+        public static Func<IDataReader, T> GetRowParser<T>(this IDataReader reader, Type concreteType = null,
+            int startIndex = 0, int length = -1, bool returnNullIfFirstMissing = false)
+        {
+            if (concreteType == null) concreteType = typeof(T);
+            var func = GetDeserializer(concreteType, reader, startIndex, length, returnNullIfFirstMissing);
+            if (concreteType.IsValueType())
+            {
+                return _ => (T)func(_);
+            }
+            else
+            {
+                return (Func<IDataReader, T>)(Delegate)func;
+            }
+        }
     }
 }

Dapper/SqlMapper.cs

@@ -2651,7 +2651,8 @@ public static void SetTypeMap(Type type, ITypeMap map)
             Type type, IDataReader reader, int startBound = 0, int length = -1, bool returnNullIfFirstMissing = false
         )
         {
-            var dm = new DynamicMethod($"Deserialize{Guid.NewGuid()}", typeof(object), new[] { typeof(IDataReader) }, true);
+            var returnType = type.IsValueType() ? typeof(object) : type;
+            var dm = new DynamicMethod($"Deserialize{Guid.NewGuid()}", returnType, new[] { typeof(IDataReader) }, true);
             var il = dm.GetILGenerator();
             il.DeclareLocal(typeof(int));
             il.DeclareLocal(type);
@@ -2958,7 +2959,8 @@ public static void SetTypeMap(Type type, ITypeMap map)
             }
             il.Emit(OpCodes.Ret);
 
-            return (Func<IDataReader, object>)dm.CreateDelegate(typeof(Func<IDataReader, object>));
+            var funcType = System.Linq.Expressions.Expression.GetFuncType(typeof(IDataReader), returnType);
+            return (Func<IDataReader, object>)dm.CreateDelegate(funcType);
         }
 
         private static void FlexibleConvertBoxedFromHeadOfStack(ILGenerator il, Type from, Type to, Type via)

Dapper/project.json

@@ -5,7 +5,7 @@
   "licenseUrl": "http://www.apache.org/licenses/LICENSE-2.0",
   "summary": "A high performance Micro-ORM",
   "description": "A high performance Micro-ORM supporting SQL Server, MySQL, Sqlite, SqlCE, Firebird etc..",
-  "version": "1.50-beta6",
+  "version": "1.50-beta7",
   "title": "Dapper dot net",
   "tags": [ "orm", "sql", "micro-orm" ],
   "copyright": "2015 Stack Exchange, Inc.",