Covariant returns

Author: alex-kulakov

Orm/Xtensive.Orm/Arithmetic/Internal/NullableArithmetic.cs

@@ -82,10 +82,7 @@ public override bool IsSigned
     }
 
     /// <inheritdoc/>
-    protected override IArithmetic<T?> CreateNew(ArithmeticRules rules)
-    {
-      return new NullableArithmetic<T>(Provider, rules);
-    }
+    protected override NullableArithmetic<T> CreateNew(ArithmeticRules rules) => new(Provider, rules);
 
 
     // Constructors

Orm/Xtensive.Orm/Arithmetic/Internal/PrimitiveArithmetics.tt

@@ -1,4 +1,4 @@
-<#@ template language="C#" #>
+<#@ template language="C#" #>
 <#@ assembly name="System.Core" #>
 <#@ import namespace="System.Linq" #>
 // Copyright (C) 2008 Xtensive LLC.
@@ -146,10 +146,7 @@ foreach (var type in types) {
     }
 
     /// <inheritdoc/>
-    protected override IArithmetic<<#= primitiveName #>> CreateNew(ArithmeticRules rules)
-    {
-      return new <#= className #>(Provider, rules);
-    }
+    protected override <#= className #> CreateNew(ArithmeticRules rules) => new(Provider, rules);
 
 
     // Constructors

Orm/Xtensive.Orm/Collections/ExtensionCollection.cs

@@ -106,10 +106,13 @@ public override void Lock(bool recursive)
     #region ICloneable methods
 
     /// <inheritdoc/>
-    public object Clone()
-    {
-      return new ExtensionCollection(this);
-    }
+    object ICloneable.Clone() => Clone();
+
+    /// <summary>
+    /// Creates a new object that is a copy of the current instance.
+    /// </summary>
+    /// <returns>A new object that is a copy of this instance.</returns>
+    public ExtensionCollection Clone() => new(this);
 
     #endregion
 

Orm/Xtensive.Orm/Collections/TypeRegistry.cs

@@ -151,14 +151,14 @@ public override void Lock(bool recursive)
 
     #region ICloneable members
 
+    /// <inheritdoc/>
+    object ICloneable.Clone() => Clone();
+
     /// <summary>
     /// Clones this instance.
     /// </summary>
     /// <returns></returns>
-    public virtual object Clone()
-    {
-      return new TypeRegistry(this);
-    }
+    public virtual TypeRegistry Clone() => new TypeRegistry(this);
 
     #endregion
 

Orm/Xtensive.Orm/Comparison/CastingComparer.cs

@@ -40,7 +40,7 @@ public AsymmetricCompareHandler(Func<TSource, TSecond, int> baseCompare)
     private readonly AdvancedComparer<TSource> sourceComparer;
 
     /// <inheritdoc/>
-    protected override IAdvancedComparer<TTarget> CreateNew(ComparisonRules rules)
+    protected override CastingComparer<TSource, TTarget> CreateNew(ComparisonRules rules)
       => new CastingComparer<TSource, TTarget>(sourceComparer.ApplyRules(rules));
 
     /// <inheritdoc/>

Orm/Xtensive.Orm/Comparison/Internals/ArrayComparer.cs

@@ -13,8 +13,7 @@ namespace Xtensive.Comparison
   internal sealed class ArrayComparer<T> : WrappingComparer<T[], T>, 
     ISystemComparer<T[]>
   {
-    protected override IAdvancedComparer<T[]> CreateNew(ComparisonRules rules)
-      => new ArrayComparer<T>(Provider, ComparisonRules.Combine(rules));
+    protected override ArrayComparer<T> CreateNew(ComparisonRules rules) => new(Provider, ComparisonRules.Combine(rules));
 
     public override int Compare(T[] x, T[] y)
     {

Orm/Xtensive.Orm/Comparison/Internals/AssemblyComparer.cs

@@ -14,8 +14,7 @@ namespace Xtensive.Comparison
   internal sealed class AssemblyComparer: WrappingComparer<Assembly, string>,
     ISystemComparer<Assembly>
   {
-    protected override IAdvancedComparer<Assembly> CreateNew(ComparisonRules rules)
-      => new AssemblyComparer(Provider, ComparisonRules.Combine(rules));
+    protected override AssemblyComparer CreateNew(ComparisonRules rules) => new(Provider, ComparisonRules.Combine(rules));
 
     public override int Compare(Assembly x, Assembly y)
     {

Orm/Xtensive.Orm/Comparison/Internals/BaseComparerWrapper.cs

@@ -14,8 +14,7 @@ namespace Xtensive.Comparison
   internal class BaseComparerWrapper<T, TBase>: WrappingComparer<T, TBase>
     where T: TBase
   {
-    protected override IAdvancedComparer<T> CreateNew(ComparisonRules rules)
-      => new BaseComparerWrapper<T, TBase>(Provider, ComparisonRules.Combine(rules));
+    protected override BaseComparerWrapper<T, TBase> CreateNew(ComparisonRules rules) => new(Provider, ComparisonRules.Combine(rules));
 
     public override int Compare(T x, T y) => BaseComparer.Compare(x, y);
 

Orm/Xtensive.Orm/Comparison/Internals/BooleanComparer.cs

@@ -14,7 +14,7 @@ namespace Xtensive.Comparison
   [Serializable]
   internal sealed class BooleanComparer : ValueTypeComparer<bool>
   {
-    protected override IAdvancedComparer<bool> CreateNew(ComparisonRules rules) => new BooleanComparer(Provider, ComparisonRules.Combine(rules));
+    protected override BooleanComparer CreateNew(ComparisonRules rules) => new(Provider, ComparisonRules.Combine(rules));
 
     public override bool GetNearestValue(bool value, Direction direction)
     {

Orm/Xtensive.Orm/Comparison/Internals/ByteComparer.cs

@@ -12,8 +12,7 @@ namespace Xtensive.Comparison
   [Serializable]
   internal sealed class ByteComparer : ValueTypeComparer<byte>
   {
-    protected override IAdvancedComparer<byte> CreateNew(ComparisonRules rules)
-      => new ByteComparer(Provider, ComparisonRules.Combine(rules));
+    protected override ByteComparer CreateNew(ComparisonRules rules) => new(Provider, ComparisonRules.Combine(rules));
 
 
     // Constructors