Initialize a Dictionary with values in C# 2.0

Question

In C# 2.0 we can initialize arrays and lists with values like this:

int[] a = { 0, 1, 2, 3 };
int[,] b = { { 0, 1 }, { 1, 2 }, { 2, 3 } };
List<int> c = new List<int>(new int[] { 0, 1, 2, 3 });

I would like to do the same with Dictionary. I know you can do it easily in C# 3.0 onwards like this:

Dictionary<int, int> d = new Dictionary<int, int> { { 0, 1 }, { 1, 2 }, { 2, 3 } };

But it doesn't work in C# 2.0. Is there any workaround for this without using Add or basing on an already existing collection?

Answer 1

But it doesn't work in C# 2.0. Is there any workaround for this without using Add or basing on an already existing collection?

No. The closest I can think of would be to write your own DictionaryBuilder type to make it simpler:

public class DictionaryBuilder<TKey, TValue>
{
    private Dictionary<TKey, TValue> dictionary
        = new Dictionary<TKey, TValue> dictionary();

    public DictionaryBuilder<TKey, TValue> Add(TKey key, TValue value)
    {
        if (dictionary == null)
        {
            throw new InvalidOperationException("Can't add after building");
        }
        dictionary.Add(key, value);
        return this;
    }

    public Dictionary<TKey, TValue> Build()
    {
        Dictionary<TKey, TValue> ret = dictionary;
        dictionary = null;
        return ret;
    }
}

Then you can use:

Dictionary<string, int> x = new DictionaryBuilder<string, int>()
    .Add("Foo", 10)
    .Add("Bar", 20)
    .Build();

This is at least a single expression still, which is useful for fields where you want to initialize at the point of declaration.