[英]How do I simulate anonymous classes in C#
我正在用C#編寫一個小型數據結構庫,並且遇到了體系結構問題。 本質上,我有一個實現訪客模式的類,並且有許多可能的訪客實現:
public interface ITreeVisitor<T, U>
{
U Visit(Nil<T> s);
U Visit(Node<T> s);
}
public abstract class Tree<T> : IEnumerable<T>
{
public readonly static Tree<T> empty = new Nil<T>();
public abstract U Accept<U>(ITreeVisitor<T, U> visitor);
}
public sealed class Nil<T> : Tree<T>
{
public override U Accept<U>(ITreeVisitor<T, U> visitor) { return visitor.Visit(this); }
}
public sealed class Node<T> : Tree<T>
{
public Tree<T> Left { get; set; }
public T Value { get; set; }
public Tree<T> Right { get; set; }
public override U Accept<U>(ITreeVisitor<T, U> visitor) { return visitor.Visit(this); }
}
每當我想傳遞訪問者時,我都必須創建一個訪問者類,實現該接口,然后像這樣傳遞它:
class InsertVisitor<T> : ITreeVisitor<T, Tree<T>> where T : IComparable<T>
{
public T v { get; set; };
public Tree<T> Visit(Nil<T> s)
{
return new Node<T>() { Left = Tree<T>.empty, Value = v, Right = Tree<T>.empty };
}
public Tree<T> Visit(Node<T> s)
{
switch (v.CompareTo(s.Value))
{
case -1: return new Node<T>() { Left = Insert(v, s.Left), Value = s.Value, Right = s.Right };
case 1: return new Node<T>() { Left = s.Left, Value = s.Value, Right = Insert(v, s.Right) };
default: return s;
}
}
}
public static Tree<T> Insert<T>(T value, Tree<T> tree) where T : IComparable<T>
{
return tree.Accept<Tree<T>>(new InsertVisitor<T>() { v = value });
}
我不喜歡編寫那么多樣板代碼,因為當訪問者實現的數量非常少時,它會變得非常混亂。
我想寫一些類似於匿名類Java (概念代碼)的東西:
public static Tree<T> Insert<T>(T v, Tree<T> tree) where T : IComparable<T>
{
return tree.Accept<Tree<T>>(new InsertVisitor<T>()
{
public Tree<T> Visit(Nil<T> s) { return new Node<T>() { Left = Tree<T>.empty, Value = v, Right = Tree<T>.empty }; }
public Tree<T> Visit(Node<T> s)
{
switch (v.CompareTo(s.Value))
{
case -1: return new Node<T>() { Left = Insert(v, s.Left), Value = s.Value, Right = s.Right };
case 1: return new Node<T>() { Left = s.Left, Value = s.Value, Right = Insert(v, s.Right) };
default: return s;
}
}
};
}
有沒有辦法用C#中的接口實現模擬匿名類?
您可以將類的“行為”部分從針對接口定義的方法更改為在適當的時候調用的委托,並通過傳遞新的委托來創建新的訪問者-從而招募匿名函數來完成匿名類的工作。
草圖代碼(未經測試,您可以根據需要進行清理):
class CustomVisitor<T> : ITreeVisitor<T, Tree<T>> where T : IComparable<T>
{
public T v { get; set; };
public Func<Nil<T>, Tree<T>> VisitNil { get; set; }
public Func<Node<T>, Tree<T>> VisitNode { get; set; }
public Tree<T> Visit(Nil<T> s) { return VisitNil(s); }
public Tree<T> Visit(Node<T> s) { return VisitNode(s); }
}
public static Tree<T> Insert<T>(T v, Tree<T> tree) where T : IComparable<T>
{
return tree.Accept<Tree<T>>(new CustomVisitor<T> {
VisitNil = s =>
return new Node<T>() { Left = Tree<T>.empty, Value = v, Right = Tree<T>.empty }; }
VisitNode = s =>
{
switch (v.CompareTo(s.Value))
{
case -1: return new Node<T>() { Left = Insert(v, s.Left), Value = s.Value, Right = s.Right };
case 1: return new Node<T>() { Left = s.Left, Value = s.Value, Right = Insert(v, s.Right) };
default: return s;
}
}
});
}
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