Boost efficiency of Rooted IRecursiveParent.Children

And fix a bug found by this change making a test fail.

Author: AArnott

src/ImmutableObjectGraph.Generation/CodeGen+RootedStructGen.cs

@@ -743,19 +743,15 @@ protected MethodDeclarationSyntax CreateParentedNodeMethod()
             protected PropertyDeclarationSyntax[] CreateChildrenProperties()
             {
                 return new PropertyDeclarationSyntax[] {
-                    // IEnumerable<IRecursiveType> IRecursiveParent.Children { get; }
+                    // IEnumerable<IRecursiveType> IRecursiveParent.Children => this.greenNode.Children;
                     SyntaxFactory.PropertyDeclaration(Syntax.IEnumerableOf(Syntax.GetTypeSyntax(typeof(IRecursiveType))), nameof(IRecursiveParent.Children))
                         .WithExplicitInterfaceSpecifier(SyntaxFactory.ExplicitInterfaceSpecifier(Syntax.GetTypeSyntax(typeof(IRecursiveParent))))
-                        .AddAccessorListAccessors(SyntaxFactory.AccessorDeclaration(
-                            SyntaxKind.GetAccessorDeclaration,
-                            SyntaxFactory.Block(
-                                // return System.Linq.Enumerable.Cast<IRecursiveType>(this.Children);
-                                SyntaxFactory.ReturnStatement(
-                                    Syntax.EnumerableExtension(
-                                        SyntaxFactory.GenericName(nameof(Enumerable.Cast))
-                                            .AddTypeArgumentListArguments(Syntax.GetTypeSyntax(typeof(IRecursiveType))),
-                                        Syntax.ThisDot(this.applyTo.RecursiveParent.RecursiveField.NameAsProperty),
-                                        SyntaxFactory.ArgumentList()))))),
+                        .WithExpressionBody(SyntaxFactory.ArrowExpressionClause(
+                            SyntaxFactory.MemberAccessExpression(
+                                SyntaxKind.SimpleMemberAccessExpression,
+                                Syntax.ThisDot(GreenNodeFieldName),
+                                this.applyTo.RecursiveParent.RecursiveField.NameAsProperty)))
+                        .WithSemicolonToken(SyntaxFactory.Token(SyntaxKind.SemicolonToken)),
                     // IEnumerable<TRootedRecursiveType> IRecursiveParent<TRootedRecursiveType>.Children { get; }
                     SyntaxFactory.PropertyDeclaration(Syntax.IEnumerableOf(this.rootedRecursiveType), nameof(IRecursiveParent<IRecursiveType>.Children))
                         .WithExplicitInterfaceSpecifier(SyntaxFactory.ExplicitInterfaceSpecifier(CreateIRecursiveParentOfTSyntax(this.rootedRecursiveType)))

src/ImmutableObjectGraph/RecursiveTypeExtensions.cs

@@ -292,10 +292,10 @@ public static IEnumerable<TRecursiveType> GetSelfAndDescendentsBreadthFirst<TRec
                 var visiting = nodesToVisit.Dequeue();
                 yield return visiting;
 
-                var visitingAsParent = visiting as IRecursiveParent;
+                var visitingAsParent = visiting as IRecursiveParent<TRecursiveType>;
                 if (visitingAsParent != null && visitingAsParent.Children != null)
                 {
-                    foreach (TRecursiveType child in visitingAsParent.Children)
+                    foreach (var child in visitingAsParent.Children)
                     {
                         nodesToVisit.Enqueue(child);
                     }