Question

I have this method

public string DictionaryToString<T, U>(Dictionary<T, U> dict)
{
  var valueStrings = dict.Select(x => x.Key.ToString() + ": " + x.Value.ToString());
  return String.Join("\n", valueStrings);
}

And I have this object that I want to pass into it

if ((value !=null) && value.GetType().IsGenericType &&
  value.GetType().GetGenericTypeDefinition() == typeof (Dictionary<,>))
{
   var castValue = value as Dictionary<,>; // this cast does not work
   return DictionaryToString(castValue);
}
else
{
  return value.ToString();
}

I can use reflection code like this in .Net 4.5

var targetMethodInfo = typeof(MyType).GetMethod("DictionaryToString");
var valueTypeArgs = value.GetType().GenericTypeArguments;
var genericMethod = targetMethodInfo.MakeGenericMethod(valueTypeArgs);
var result = genericMethod.Invoke(this, new[] {value });
return result.ToString();

ButType.GenericTypeArguments is new in .Net 4.5. So how can I do that cast in .Net 4.0?

Answer 1

You are only calling ToString on the key and value, so simply have this method take an IDictionary (non-generic), you are not using anything in there that is type-specific to T or U.

You can then simply cast all arguments to IDictionary:

var d = arg as IDictionary;

if (d != null)
{
    var res = DictionaryToString(d);
}

You may also need to amend the DictionaryToString implementation:

static string DictionaryToString(IDictionary d)
{
    var vals = new List<string>();

    foreach (DictionaryEntry de in d)
    {
        vals.Add(de.Key.ToString() + ": " + de.Value.ToString());
    }

    return String.Join("\n", vals);
}

Alternatively, if you really want to use LINQ, you could try casting to dynamic (it isn’t possible to cast to anything else as this could be a generic dictionary (KeyValuePair<>) or non-generic hashtable (DictionaryEntry)):

var valueStrings = d.Cast<dynamic>().Select(de => de.Key.ToString() + ": " + de.Value.ToString());
return string.Join("\n", valueStrings);

This basically “duck types” the existence of the Key and Value properties.