using System;

using System.Collections.Generic;

using System.Linq;

​

public static class Extensions

{

    public static void Write<K, V>(this IEnumerable<KeyValuePair<K, V>> me, string label)

    {

        Console.WriteLine();

        Console.WriteLine($"---- {label} ----");

        foreach(var kvp in me)

        {

            Console.WriteLine($"[{kvp.Key}]={kvp.Value}");

        }

    }

    public static IEnumerable<KeyValuePair<K, V>> ToDictionaryNoDups<K, V>(this IEnumerable<V> me, Func<V, K> selector) where K : notnull

    {

        Dictionary<K, V> dictionary = new();

        foreach(V v in me)

        {

            K key = selector.Invoke(v);

            if(dictionary.ContainsKey(key))

            {

                dictionary[key] = v;

            }

            else

            {

                dictionary.Add(key, v);

            }

        }

        return dictionary;

    }

}

​

public record Widget

{

    public string Name { get; set; }

    public string Value { get; set; }

}

​

public class WidgetComparer : IEqualityComparer<KeyValuePair<string, Widget>>

{

    private StringComparer _stringComparer;

    public WidgetComparer(StringComparer stringComparer = null)

    {

        _stringComparer = stringComparer ?? StringComparer.InvariantCultureIgnoreCase;

    }

    public bool Equals(KeyValuePair<string, Widget> me, KeyValuePair<string, Widget> other)

    {

        return _stringComparer.Compare(me.Key, other.Key) == 0;

    }

    public int GetHashCode(KeyValuePair<string, Widget> me)

    {

        return HashCode.Combine(me.Key.GetHashCode());

    }

    public readonly static IEqualityComparer<KeyValuePair<string, Widget>> WidgetComparerInvariantCulture = new WidgetComparer(StringComparer.InvariantCulture);

    public readonly static IEqualityComparer<KeyValuePair<string, Widget>> WidgetComparerInvariantCultureIgnoreCase = new WidgetComparer(StringComparer.InvariantCultureIgnoreCase);

​

}

​

public class Program

{

    public static void Main()

    {

        Widget[] widgets1 = new Widget[] { 

            new() { Name = "a", Value = "A1" }, 

            new() { Name = "b", Value = "B1" },

            new() { Name = "a", Value = "AA1" }

        };

        Widget[] widgets2 = new Widget[] { 

            new() { Name = "b", Value = "B2" }, 

            new() { Name = "c", Value = "C2" },

            new() { Name = "d", Value = "D2" }

        };

​

        Dictionary<string, Widget> v1 = new(widgets1.ToDictionaryNoDups(x => x.Name));

        Dictionary<string, Widget> v2 = new(widgets2.ToDictionaryNoDups(x => x.Name));

        v1.Write("v1");

        v2.Write("v2");

​

        Dictionary<string, Widget> all = new(v1.Union(v2).Select(x => x.Value).ToDictionaryNoDups(x => x.Name));

        all.Write("all - no dups");

        all.Except(v1, WidgetComparer.WidgetComparerInvariantCultureIgnoreCase).Write("all except v1");

        all.Except(v2, WidgetComparer.WidgetComparerInvariantCultureIgnoreCase).Write("all except v2");

        v1.Union(v2, WidgetComparer.WidgetComparerInvariantCultureIgnoreCase).Write("widgets1 union widgets2");

    }

}