Question

I’m doing some generic object comparison, using reflection and recursion. The recursive method needs some type information in each step, which is given by the caller. At one point I know that the next property is a Dictionary<T,U>, and I want to send the correct type. I came up with this:

Type dictionaryType = typeof (IDictionary<,>).MakeGenericType(new [] {keyType.PropertyType, typeof(ValueType)});

Where keyType and ValueType are types found out earlier. However, this type does not implement the IDictionary<KeyType, ValueType> interface, according to dictionaryType.GetInterfaces(). Why? It looks like it should…

Answer 1

Because the type IS IDictionary<KeyType, ValueType>. The GetInterfaces method only promises to return An array of Type objects representing all the interfaces implemented or inherited by the current Type. Since IDictionary<> does not (and indeed cannot) implement itself, the return value is legitimately all interfaces it inherits.

Using Dictionary<,> as an arbitrary class that implements IDictionary<,>, the following would be more appropriate:

Type dictionaryType = typeof (Dictionary<,>).MakeGenericType(new [] {keyType.PropertyType, typeof(ValueType)});