using System;

using System.Collections.Generic;

using System.IO;

using YamlDotNet.Serialization;

​

public class UniqueKeysDictionary<TKey, TValue> : Dictionary<TKey, TValue>, IDictionary<TKey, TValue>

{

    TValue IDictionary<TKey, TValue>.this[TKey key]

    {

        get { return base[key]; }

        set { base.Add(key, value); }

    }

}

​

public class Program

{

    public static void Main()

    {

        var yaml = @"

foo: bar

foo: baz

";

        var deserializer = new Deserializer();

        var data = deserializer.Deserialize<UniqueKeysDictionary<string, string>>(new StringReader(yaml));

        foreach(var entry in data)

        {

            Console.WriteLine("{0}: {1}", entry.Key, entry.Value);

        }

    }

}