So, I would like to write something like this:

var d = new ImmutableDictionary<string, int> { { "a", 1 }, { "b", 2 } };

(using ImmutableDictionary from System.Collections.Immutable). It seems like a straightforward usage as I am declaring all the values upfront -- no mutation there. But this gives me error:

The type 'System.Collections.Immutable.ImmutableDictionary<TKey,TValue>' has no constructors defined

How I am supposed to create a new immutable dictionary with static content?