Added LastOfType and LastOfTypeOrDefault.

Author: MrKWatkins

src/MrKWatkins.Ast.Tests/ChildrenTests.cs

@@ -522,6 +522,38 @@ public void FirstOfType()
             .WithMessage("Expected ANode to have a child of type CNode but found none.");
     }
 
+    [Test]
+    public void LastOfTypeOrDefault()
+    {
+        var a = new ANode();
+        var b1 = new BNode();
+        var b2 = new BNode();
+        
+        var parent = new ANode(b1, a, b2);
+
+        var @default = new CNode();
+
+        parent.Children.LastOfTypeOrDefault<ANode>().Should().BeSameAs(a);
+        parent.Children.LastOfTypeOrDefault<BNode>().Should().BeSameAs(b2);
+        parent.Children.LastOfTypeOrDefault(@default).Should().BeSameAs(@default);
+    }
+    
+    [Test]
+    public void LastOfType()
+    {
+        var a = new ANode();
+        var b1 = new BNode();
+        var b2 = new BNode();
+        
+        var parent = new ANode(b1, a, b2);
+
+        parent.Children.LastOfType<ANode>().Should().BeSameAs(a);
+        parent.Children.LastOfType<BNode>().Should().BeSameAs(b2);
+        parent.Children.Invoking(c => c.LastOfType<CNode>())
+            .Should().Throw<InvalidOperationException>()
+            .WithMessage("Expected ANode to have a child of type CNode but found none.");
+    }
+    
     [Test]
     public void SingleOfTypeOrDefault()
     {

src/MrKWatkins.Ast/Children.cs

@@ -283,6 +283,39 @@ public TChild FirstOfType<TChild>()
         where TChild : TNode =>
         FirstOfTypeOrDefault<TChild>() ?? throw new InvalidOperationException($"Expected {parent.GetType().SimpleName()} to have a child of type {typeof(TChild).SimpleName()} but found none.");
 
+    /// <summary>
+    /// Returns the last node in the collection of the specified type or a specified default if it doesn't contain any nodes of the specified type.
+    /// </summary>
+    /// <typeparam name="TChild">The type of the node to return.</typeparam>
+    /// <param name="default">The default value to return if the collection does not contain any nodes of type <typeparamref name="TChild"/>.</param>
+    /// <returns>The last node if it is of the specified type or <paramref name="default"/> if it doesn't contain any nodes of the specified type.</returns>
+    [Pure]
+    public TChild? LastOfTypeOrDefault<TChild>(TChild? @default = null)
+        where TChild : TNode
+    {
+        // Manually iterating for performance. Looks like LINQ's Reverse() doesn't optimise for IList<T>.
+        for (var f = Count - 1; f >= 0; f--)
+        {
+            if (nodes[f] is TChild child)
+            {
+                return child;
+            }
+        }
+
+        return @default;
+    }
+
+    /// <summary>
+    /// Returns the last node in the collection of the specified type or throws otherwise.
+    /// </summary>
+    /// <typeparam name="TChild">The type of the node to return.</typeparam>
+    /// <returns>The last node if it is of the specified type.</returns>
+    /// <exception cref="InvalidOperationException">If the collection doesn't contain any nodes of the specified type.</exception>
+    [Pure]
+    public TChild LastOfType<TChild>()
+        where TChild : TNode =>
+        LastOfTypeOrDefault<TChild>() ?? throw new InvalidOperationException($"Expected {parent.GetType().SimpleName()} to have a child of type {typeof(TChild).SimpleName()} but found none.");
+
     /// <summary>
     /// Returns the only node in the collection of the specified type. Returns the specified default if there are no nodes in the collection of the
     /// specified type. Throws if there are multiple nodes in the collection of the specified type.