c# - 通用嵌套类型 : cannot convert from X to X

Question

我正在编写一个用于处理无向图的类，遇到了以下编译时错误:

The best overloaded method match for 'Dictionary.EdgeCollection>.Add(TVertex, UndirectedGraph.EdgeCollection)' has some invalid arguments

Argument 2: cannot convert from UndirectedGraph<TVertex,TEdge>.AdjacentEdgeCollection<TVertex,TEdge> to UndirectedGraph<TVertex,TEdge>.AdjacentEdgeCollection<TVertex,TEdge>

我可以将问题简化为以下示例:

public class UndirectedGraph<TVertex, TEdge>
{
    Dictionary<TVertex, EdgeCollection<TVertex, TEdge>> edges;

    class VertexCollection<TVertex, TEdge>
    {
        UndirectedGraph<TVertex, TEdge> graph;

        public VertexCollection(UndirectedGraph<TVertex, TEdge> graph)
        { this.graph = graph; }

        public void Add(TVertex value)
        {
            // Argument 2: cannot convert
            // from 'UndirectedGraph<TVertex,TEdge>.AdjacentEdgeCollection<TVertex,TEdge>'
            //   to 'UndirectedGraph<TVertex,TEdge>.AdjacentEdgeCollection<TVertex,TEdge>'
            this.graph.edges.Add(value, new EdgeCollection<TVertex, TEdge>(this.graph));
        }
    }

    class EdgeCollection<TVertex, TEdge>
    {
        public EdgeCollection(UndirectedGraph<TVertex, TEdge> graph) { }
    }
}

请注意 TVertex和 TEdge在嵌套类中不同于 TVertex和 TEdge在外部类中，我收到警告说我应该重命名它们。我可以这样做，但这不会影响错误。我觉得这个fragment的目的很明确，那我怎么让它做我想做的事，我的思路错在哪里呢？

Answer 1

你确定有3个TVertex类型参数和3个TEdge类型参数吗？在我看来，这三个都是相同的，您需要的是以下内容:

public class UndirectedGraph<TVertex, TEdge>
{
    Dictionary<TVertex, EdgeCollection> edges;

    class VertexCollection
    {
        UndirectedGraph<TVertex, TEdge> graph;

        public VertexCollection(UndirectedGraph<TVertex, TEdge> graph)
        { this.graph = graph; }

        public void Add(TVertex value)
        {
            this.graph.edges.Add(value, new EdgeCollection(this.graph));
        }
    }

    class EdgeCollection
    {
        public EdgeCollection(UndirectedGraph<TVertex, TEdge> graph) { }
    }
}