object-and-collection-initializers_8.cs

using System;
using System.Collections;
using System.Collections.Generic;

namespace ExampleProject
{
    class RudimentaryMultiValuedDictionary<TKey, TValue> : IEnumerable<KeyValuePair<TKey, List<TValue>>>
    {
        private Dictionary<TKey, List<TValue>> internalDictionary = new Dictionary<TKey, List<TValue>>();

        public IEnumerator<KeyValuePair<TKey, List<TValue>>> GetEnumerator() => internalDictionary.GetEnumerator();

        IEnumerator IEnumerable.GetEnumerator() => internalDictionary.GetEnumerator();

        public List<TValue> this[TKey key]
        {
            get => internalDictionary[key];
            set => Add(key, value);
        }

        public void Add(TKey key, params TValue[] values) => Add(key, (IEnumerable<TValue>)values);

        public void Add(TKey key, IEnumerable<TValue> values)
        {
            if (!internalDictionary.TryGetValue(key, out List<TValue> storedValues))
                internalDictionary.Add(key, storedValues = new List<TValue>());

            storedValues.AddRange(values);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            RudimentaryMultiValuedDictionary<string, string> rudimentaryMultiValuedDictionary1
                = new RudimentaryMultiValuedDictionary<string, string>()
                {
                    {"Group1", "Bob", "John", "Mary" },
                    {"Group2", "Eric", "Emily", "Debbie", "Jesse" }
                };
            RudimentaryMultiValuedDictionary<string, string> rudimentaryMultiValuedDictionary2
                = new RudimentaryMultiValuedDictionary<string, string>()
                {
                    ["Group1"] = new List<string>() { "Bob", "John", "Mary" },
                    ["Group2"] = new List<string>() { "Eric", "Emily", "Debbie", "Jesse" }
                };

            Console.WriteLine("Using first multi-valued dictionary created with a collection initializer:");

            foreach(KeyValuePair<string, List<string>> group in rudimentaryMultiValuedDictionary1)
            {
                Console.WriteLine($"\r\nMembers of group {group.Key}: ");

                foreach(string member in group.Value)
                {
                    Console.WriteLine(member);
                }
            }

            Console.WriteLine("\r\nUsing second multi-valued dictionary created with a collection initializer using indexing:");

            foreach (KeyValuePair<string, List<string>> group in rudimentaryMultiValuedDictionary2)
            {
                Console.WriteLine($"\r\nMembers of group {group.Key}: ");

                foreach (string member in group.Value)
                {
                    Console.WriteLine(member);
                }
            }
        }

        /*
         * Prints:
         
            Using first multi-valued dictionary created with a collection initializer:

            Members of group Group1:
            Bob
            John
            Mary

            Members of group Group2:
            Eric
            Emily
            Debbie
            Jesse

            Using second multi-valued dictionary created with a collection initializer using indexing:

            Members of group Group1:
            Bob
            John
            Mary

            Members of group Group2:
            Eric
            Emily
            Debbie
            Jesse
         */
    }
}