descriptor API: use index rather than constantly looking up the name

Dapper/SqlMapper.DapperRow.Descriptor.cs

@@ -70,7 +70,7 @@ internal static PropertyDescriptorCollection GetProperties(DapperTable table, ID
                     {
                         var type = row != null && row.TryGetValue(names[i], out var value) && value != null
                             ? value.GetType() : typeof(object);
-                        arr[i] = new RowBoundPropertyDescriptor(type, names[i]);
+                        arr[i] = new RowBoundPropertyDescriptor(type, names[i], i);
                     }
                     return new PropertyDescriptorCollection(arr, true);
                 }
@@ -84,20 +84,22 @@ internal static PropertyDescriptorCollection GetProperties(DapperTable table, ID
             private sealed class RowBoundPropertyDescriptor : PropertyDescriptor
             {
                 private readonly Type _type;
-                public RowBoundPropertyDescriptor(Type type, string name) : base(name, null)
-                    => _type = type;
-
-                public override bool CanResetValue(object component) => false;
-                public override void ResetValue(object component) => throw new NotSupportedException();
-
+                private readonly int _index;
+                public RowBoundPropertyDescriptor(Type type, string name, int index) : base(name, null)
+                {
+                    _type = type;
+                    _index = index;
+                }
+                public override bool CanResetValue(object component) => true;
+                public override void ResetValue(object component) => ((DapperRow)component).Remove(_index);
                 public override bool IsReadOnly => false;
-                public override bool ShouldSerializeValue(object component) => true;
+                public override bool ShouldSerializeValue(object component) => ((DapperRow)component).TryGetValue(_index, out _);
                 public override Type ComponentType => typeof(DapperRow);
                 public override Type PropertyType => _type;
                 public override object GetValue(object component)
-                    => ((IDictionary<string, object>)component).TryGetValue(Name, out var val) ? val : null;
+                    => ((DapperRow)component).TryGetValue(_index, out var val) ? (val ?? DBNull.Value): DBNull.Value;
                 public override void SetValue(object component, object value)
-                    => ((IDictionary<string, object>)component)[Name] = value;
+                    => ((DapperRow)component).SetValue(_index, value is DBNull ? null : value);
             }
         }
     }

Dapper/SqlMapper.DapperRow.cs

@@ -40,8 +40,10 @@ private sealed class DeadValue
             }
 
             public bool TryGetValue(string key, out object value)
+                => TryGetValue(table.IndexOfName(key), out value);
+
+            internal bool TryGetValue(int index, out object value)
             {
-                var index = table.IndexOfName(key);
                 if (index < 0)
                 { // doesn't exist
                     value = null;
@@ -146,8 +148,10 @@ IEnumerator IEnumerable.GetEnumerator()
             }
 
             bool IDictionary<string, object>.Remove(string key)
+                => Remove(table.IndexOfName(key));
+
+            internal bool Remove(int index)
             {
-                int index = table.IndexOfName(key);
                 if (index < 0 || index >= values.Length || values[index] is DeadValue) return false;
                 values[index] = DeadValue.Default;
                 return true;
@@ -177,6 +181,10 @@ private object SetValue(string key, object value, bool isAdd)
                     // then semantically, this value already exists
                     throw new ArgumentException("An item with the same key has already been added", nameof(key));
                 }
+                return SetValue(index, value);
+            }
+            internal object SetValue(int index, object value)
+            {
                 int oldLength = values.Length;
                 if (oldLength <= index)
                 {

UIBindingTest/BindingForm.cs

@@ -10,10 +10,12 @@ public BindingForm()
         {
             InitializeComponent();
 
+            SuspendLayout();
             using (var conn = new SqlConnection("Data Source=.;Initial Catalog=master;Integrated Security=SSPI"))
             {
                 mainGrid.DataSource = conn.Query("select * from sys.objects").AsList();
             }
+            ResumeLayout();
         }
     }
 }