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?

What's constraining you to still use C# 2? Life is so much better from C# 3 onwards, even if you're targeting .NET 2, that it's worth trying to muse a more recent compiler... — Jon Skeet
– Jon Skeet, Commented Jul 19, 2013 at 6:04
Ha ha, I was wondering if I should ask for not answering the way you did. Working with C# 2 is a requirement which I can't do much about. I know newer C# versions make things easier, but since I already ran into this problem, I figured I would ask out of curiosity. — S_F
– S_F, Commented Jul 19, 2013 at 6:10
I'm intrigued as to why there's this requirement though. Being limited to .NET 2.0 I can understand, but C# 2 seems an odder requirement. — Jon Skeet
– Jon Skeet, Commented Jul 19, 2013 at 6:13

It'sNotALie. · Accepted Answer · 2013-07-19 07:42:37Z

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.

Skeet, your fluent syntax wouldn't work because Add doesn't return this;.
@Mechanical Object: Thanks for fixing the quote, but please don't change the semantics of code in other people's answers without checking first. I very deliberately have the code the way it is: I would consider it an error to add the same key multiple times; I don't want to silently ignore it. (An alternative would be to use the indexer, which would just overwrite the old entry instead - again, that would be silently hiding a problem though.)

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