How can I create a new instance of ImmutableDictionary?

Question

I would like to write something like this:

var d = new ImmutableDictionary { { \"a\", 1 }, { \"b\", 2 } };

(using

Answer 1

So far I like this most:

var d = new Dictionary { { "a", 1 }, { "b", 2 } }.ToImmutableDictionary();