Use C#9 Covariant return types feature for Clone() implementation for more type safety

Author: SergeiPavlov

Orm/Xtensive.Orm.Tests.Sql/CloneTests.cs

@@ -36,7 +36,7 @@ public void SetUp()
     public void SqlExpressionCloneTest()
     {
       SqlExpression e = SqlDml.Literal(1);
-      SqlExpression eClone = (SqlExpression) e.Clone();
+      SqlExpression eClone = e.Clone();
       Assert.AreNotEqual(e, eClone);
       Assert.AreEqual(e.NodeType, eClone.NodeType);
     }

Orm/Xtensive.Orm/Orm/Upgrade/Internals/CatalogCloner.cs

@@ -84,7 +84,7 @@ private void CloneSchemas(Catalog newCatalog, Catalog source, Dictionary<string,
     private void CloneAssertions(Schema newSchema, Schema sourceSchema)
     {
       foreach (var assertion in sourceSchema.Assertions) {
-        var newAssertion = newSchema.CreateAssertion(assertion.Name, (SqlExpression)assertion.Condition.Clone(), assertion.IsDeferrable, assertion.IsInitiallyDeferred);
+        var newAssertion = newSchema.CreateAssertion(assertion.Name, assertion.Condition.Clone(), assertion.IsDeferrable, assertion.IsInitiallyDeferred);
         CopyDbName(newAssertion, assertion);
       }
     }
@@ -113,9 +113,9 @@ private void CloneDomains(Schema newSchema, Schema sourceSchema, Dictionary<Coll
         if (sourceDomain.Collation!=null)
           newDomain.Collation = collationsMap[sourceDomain.Collation];
         if (sourceDomain.DefaultValue!=null)
-          newDomain.DefaultValue = (SqlExpression)sourceDomain.DefaultValue.Clone();
+          newDomain.DefaultValue = sourceDomain.DefaultValue.Clone();
         foreach (var domainConstraint in sourceDomain.DomainConstraints) {
-          var newConstraint = newDomain.CreateConstraint(domainConstraint.Name, (SqlExpression) domainConstraint.Condition.Clone());
+          var newConstraint = newDomain.CreateConstraint(domainConstraint.Name, domainConstraint.Condition.Clone());
           CopyDbName(newConstraint, domainConstraint);
         }
       }
@@ -181,7 +181,7 @@ private void CloneTableColumns(Table newTable, Table sourceTable, Dictionary<Col
         CopyDbName(newColumn, sourceTableColumn);
 
         if (sourceTableColumn.DefaultValue!=null)
-          newColumn.DefaultValue = (SqlExpression) sourceTableColumn.DefaultValue.Clone();
+          newColumn.DefaultValue = sourceTableColumn.DefaultValue.Clone();
 
         var schema = newTable.Schema;
         if (sourceTableColumn.Collation!=null) {
@@ -196,7 +196,7 @@ private void CloneTableColumns(Table newTable, Table sourceTable, Dictionary<Col
         if (sourceTableColumn.Domain!=null)
           newColumn.Domain = schema.Domains[sourceTableColumn.Domain.Name];
         if (sourceTableColumn.Expression!=null)
-          newColumn.Expression = (SqlExpression) sourceTableColumn.Expression.Clone();
+          newColumn.Expression = sourceTableColumn.Expression.Clone();
         newColumn.IsNullable = sourceTableColumn.IsNullable;
         newColumn.IsPersisted = sourceTableColumn.IsPersisted;
         if (sourceTableColumn.SequenceDescriptor!=null)
@@ -251,7 +251,7 @@ private void CloneIndex(DataTable newTable, Index sourceIndex)
         ft.IsUnique = ftIndex.IsUnique;
         ft.UnderlyingUniqueIndex = ftIndex.UnderlyingUniqueIndex;
         if (ftIndex.Where!=null)
-          ft.Where = (SqlExpression) ftIndex.Where.Clone();
+          ft.Where = ftIndex.Where.Clone();
         ClonePartitionDescriptor(ft, sourceIndex);
         return;
       }
@@ -269,7 +269,7 @@ private void CloneIndex(DataTable newTable, Index sourceIndex)
         spatial.IsClustered = spatialIndex.IsClustered;
         spatial.IsUnique = spatialIndex.IsUnique;
         if (spatialIndex.Where!=null)
-          spatial.Where = (SqlExpression) spatialIndex.Where.Clone();
+          spatial.Where = spatialIndex.Where.Clone();
         ClonePartitionDescriptor(spatialIndex, sourceIndex);
         return;
       }
@@ -283,7 +283,7 @@ private void CloneIndex(DataTable newTable, Index sourceIndex)
       index.IsUnique = sourceIndex.IsUnique;
       index.IsClustered = sourceIndex.IsClustered;
       if (sourceIndex.Where!=null)
-        index.Where = (SqlExpression) sourceIndex.Where.Clone();
+        index.Where = sourceIndex.Where.Clone();
       index.NonkeyColumns.AddRange(GetNonKeyColumns(newTable, sourceIndex));
       index.IsBitmap = sourceIndex.IsBitmap;
       ClonePartitionDescriptor(index, sourceIndex);
@@ -319,7 +319,7 @@ private void CloneTableConstraint(Table newTable, TableConstraint sourceConstrai
     {
       var checkConstraint = sourceConstraint as CheckConstraint;
       if (checkConstraint!=null) {
-        var c = newTable.CreateCheckConstraint(checkConstraint.Name, (SqlExpression) checkConstraint.Condition.Clone());
+        var c = newTable.CreateCheckConstraint(checkConstraint.Name, checkConstraint.Condition.Clone());
         CopyDbName(c, checkConstraint);
         return;
       }

Orm/Xtensive.Orm/Sql/Ddl/Actions/SqlSetDefault.cs

@@ -17,7 +17,7 @@ public class SqlSetDefault : SqlAction
     internal override object Clone(SqlNodeCloneContext context) =>
       context.NodeMapping.TryGetValue(this, out var clone)
         ? clone
-        : context.NodeMapping[this] = new SqlSetDefault((SqlExpression) DefaultValue.Clone(context), Column);
+        : context.NodeMapping[this] = new SqlSetDefault(DefaultValue.Clone(context), Column);
 
     internal SqlSetDefault(SqlExpression defaultValue, TableColumn column)
     {

Orm/Xtensive.Orm/Sql/Dml/Expressions/SqlAggregate.cs

@@ -41,11 +41,10 @@ public override void ReplaceWith(SqlExpression expression)
       this.expression = replacingExpression.Expression;
     }
 
-    internal override object Clone(SqlNodeCloneContext context) =>
-      context.NodeMapping.TryGetValue(this, out var clone)
-        ? clone
-        : context.NodeMapping[this] = new SqlAggregate(NodeType,
-            expression.IsNullReference() ? null : (SqlExpression) expression.Clone(context), distinct);
+    internal override SqlAggregate Clone(SqlNodeCloneContext context) =>
+      context.TryGet(this) ?? context.Add(this,
+        new SqlAggregate(NodeType,
+            expression?.Clone(context), distinct));
 
     internal SqlAggregate(SqlNodeType nodeType, SqlExpression expression, bool distinct) : base(nodeType)
     {

Orm/Xtensive.Orm/Sql/Dml/Expressions/SqlArray{T}.cs

@@ -43,10 +43,9 @@ public override void ReplaceWith(SqlExpression expression)
       Values = replacingExpression.Values;
     }
 
-    internal override object Clone(SqlNodeCloneContext context) =>
-      context.NodeMapping.TryGetValue(this, out var clone)
-        ? clone
-        : context.NodeMapping[this] = new SqlArray<T>((T[]) Values.Clone());
+    internal override SqlArray Clone(SqlNodeCloneContext context) =>
+      context.TryGet(this) ?? context.Add(this,
+        new SqlArray<T>((T[]) Values.Clone()));
 
 
     // Constructors

Orm/Xtensive.Orm/Sql/Dml/Expressions/SqlBetween.cs

@@ -55,10 +55,9 @@ public override void ReplaceWith(SqlExpression expression)
       expression = replacingExpression.Expression;
     }
 
-    internal override object Clone(SqlNodeCloneContext context) =>
-      context.NodeMapping.TryGetValue(this, out var clone)
-        ? clone
-        : context.NodeMapping[this] = new SqlBetween(NodeType, (SqlExpression)expression.Clone(context), (SqlExpression)left.Clone(context), (SqlExpression)right.Clone(context));
+    internal override SqlBetween Clone(SqlNodeCloneContext context) =>
+      context.TryGet(this) ?? context.Add(this,
+        new SqlBetween(NodeType, expression.Clone(context), left.Clone(context), right.Clone(context)));
 
     internal SqlBetween(SqlNodeType nodeType, SqlExpression expression, SqlExpression left, SqlExpression right)
       : base(nodeType)

Orm/Xtensive.Orm/Sql/Dml/Expressions/SqlBinary.cs

@@ -91,12 +91,11 @@ public override void ReplaceWith(SqlExpression expression)
       Right = replacingExpression.Right;
     }
 
-    internal override object Clone(SqlNodeCloneContext context) =>
-      context.NodeMapping.TryGetValue(this, out var clone)
-        ? clone
-        : context.NodeMapping[this] = new SqlBinary(NodeType,
-            (SqlExpression) Left.Clone(context),
-            (SqlExpression) Right.Clone(context));
+    internal override SqlBinary Clone(SqlNodeCloneContext context) =>
+      context.TryGet(this) ?? context.Add(this,
+        new SqlBinary(NodeType,
+            Left.Clone(context),
+            Right.Clone(context)));
 
     public override void AcceptVisitor(ISqlVisitor visitor)
     {

Orm/Xtensive.Orm/Sql/Dml/Expressions/SqlCase.cs

@@ -105,19 +105,19 @@ public override void ReplaceWith(SqlExpression expression)
         cases.Add(pair);
     }
 
-    internal override object Clone(SqlNodeCloneContext context)
+    internal override SqlCase Clone(SqlNodeCloneContext context)
     {
       if (context.NodeMapping.TryGetValue(this, out var v)) {
-        return v;
+        return (SqlCase)v;
       }
 
-      var clone = new SqlCase(value.IsNullReference() ? null : (SqlExpression) value.Clone(context));
+      var clone = new SqlCase(value.IsNullReference() ? null : value.Clone(context));
 
       if (!@else.IsNullReference())
-        clone.Else = (SqlExpression) @else.Clone(context);
+        clone.Else = @else.Clone(context);
 
       foreach (KeyValuePair<SqlExpression, SqlExpression> pair in cases)
-        clone[(SqlExpression) pair.Key.Clone(context)] = (SqlExpression) pair.Value.Clone(context);
+        clone[pair.Key.Clone(context)] = pair.Value.Clone(context);
 
       context.NodeMapping[this] = clone;
       return clone;

Orm/Xtensive.Orm/Sql/Dml/Expressions/SqlCast.cs

@@ -22,10 +22,9 @@ public override void ReplaceWith(SqlExpression expression)
       Type = replacingExpression.Type;
     }
 
-    internal override object Clone(SqlNodeCloneContext context) =>
-      context.NodeMapping.TryGetValue(this, out var clone)
-        ? clone
-        : context.NodeMapping[this] = new SqlCast((SqlExpression) Operand.Clone(context), Type);
+    internal override SqlCast Clone(SqlNodeCloneContext context) =>
+      context.TryGet(this) ?? context.Add(this,
+        new SqlCast(Operand.Clone(context), Type));
 
     public override void AcceptVisitor(ISqlVisitor visitor)
     {

Orm/Xtensive.Orm/Sql/Dml/Expressions/SqlCollate.cs

@@ -43,10 +43,9 @@ public override void ReplaceWith(SqlExpression expression)
       collation = replacingExpression.Collation;
     }
 
-    internal override object Clone(SqlNodeCloneContext context) =>
-      context.NodeMapping.TryGetValue(this, out var clone)
-        ? clone
-        : context.NodeMapping[this] = new SqlCollate((SqlExpression)operand.Clone(context), collation);
+    internal override SqlCollate Clone(SqlNodeCloneContext context) =>
+      context.TryGet(this) ?? context.Add(this,
+        new SqlCollate(operand.Clone(context), collation));
 
     public override void AcceptVisitor(ISqlVisitor visitor)
     {