Question

I just ran into the ‘user-defined conversions to or from an interface are not allowed’ problem in C#. What I was attempting to do was create a generic Graph class that could be iterated over in a couple different ways, depending on the supported interface. So:

public class Graph<T> : IBreadthFirstSearchTree<T>, IDepthFirstSearchTree<T> {     // unnecessary details      public static explicit operator IBreadthFirstSearchTree<T>(Graph<T> g)     {         g.enumerator = new GraphEnumerator<T>(g, SortStrategy.BreadthFirst);         return g as IBreadthFirstSearchTree<T>;     }      public static explicit operator IDepthFirstSearchTree<T>(Graph<T> g)     {         g.enumerator = new GraphEnumerator<T>(g, SortStrategy.DepthFirst);         return g as IDepthFirstSearchTree<T>;     } } 

was intended for this use:

foreach (GraphNode<T> gn in myGraph as IDepthFirstSearchTree) {     // do stuff with gn } 

Anyone know how I can achieve the same syntactic results within the constraints of the language?

Answer 1

Just make your implementations of IDepthFirstSearchTree<T> and IBreadthFirstSearchTree<T> explicit implementations. That way the members won’t be available to be called directly on an expression of type Graph<T>, but using ‘as’ (or a cast) the appropriate members will be available.

I’m not sure that’s what I’d really do though – I’d probably get rid of the interfaces entirely and have:

public IEnumerable<T> IterateBreadthFirst() { ... } public IEnumerable<T> IterateDepthFirst() { ... }