CODEWITHSUNDEEP
c#generics
mcmillab
mcmillab

Reputation: 2814

returning generic Dictionary depending on type

I have a generic function that returns a Dictionary. If the key of the Dictionary is a string, I want to use the String.OrdinalIgnoreCase comparer.

This is my code:

    public static Dictionary<K,V> getDict<K,V>()
    {
        Dictionary<K,V> aDict;

        if(typeof(K)==typeof(string)) 
        {
            var stringDict = new Dictionary<string, V>(StringComparer.OrdinalIgnoreCase);
            aDict = (Dictionary<K,V>)stringDict;    // error here - can't convert.
        }
        else aDict = new Dictionary<K, V>();
// do more stuff here
        return aDict;
    }

However it tells me it

can't convert a Dictionary<string,V> to a Dictionary<K,V>.

How should I be doing this?

Upvotes: 0

Views: 75

Answers (3)

code4life
code4life

Reputation: 15794

This should work the best for you:

var stringDict = new Dictionary<K, V>(
    StringComparer.OrdinalIgnoreCase as IEqualityComparer<K>);

The problem is that the Dictionary<TKey,TValue> ctor expects an IEqualityComparer<T>. StringComparer gives you an IEqualityComparer - the non-generic variety. Once you cast your equality comparer correctly, you should be on your way.

Test code block below will trigger the expected exception:

var dict = getDict<string, int>();

dict.Add("alpha", 1);
dict.Add("Alpha", 2);  // triggers the expected duplicate key exception.

HTH...

Upvotes: 2

Yacoub Massad
Yacoub Massad

Reputation: 27871

Cast like this:

aDict = stringDict as Dictionary<K, V>;

Upvotes: 2

Alexei Levenkov
Alexei Levenkov

Reputation: 100630

One common solution - cast through intermediate cast to object:

  aDict = (Dictionary<K,V>)(object)stringDict;

Upvotes: 1

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