Initializing Lookup

Question

How do i declare a new lookup class for a property in the object initializer routine in c#?

E.g.

new Component() { ID = 1, Name = \"MOBO\", Category          


        

Answer 1

Here's my attempt on this. Make sure the key is immutable (Gist).

public class MultiValueDictionary
: Collection, ILookup
{
  public MultiValueDictionary(Func keyForItem)
    : base(new Collection(keyForItem))
  {
  }

  new Collection Items => (Collection)base.Items;

  public IEnumerable this[TKey key] => Items[key];
  public bool Contains(TKey key) => Items.Contains(key);
  IEnumerator>
    IEnumerable>.GetEnumerator() => Items.GetEnumerator();

  class Collection
  : KeyedCollection, IEnumerable, IList
  {
    Func KeyForItem { get; }

    public Collection(Func keyForItem) => KeyForItem = keyForItem;
    protected override TKey GetKeyForItem(Grouping item) => item.Key;

    public void Add(TElement item)
    {
      var key = KeyForItem(item);
      if (Dictionary != null && Dictionary.TryGetValue(key, out var collection))
        collection.Add(item);
      else
        Add(new Grouping(key) { item });
    }

    public bool Remove(TElement item)
    {
      var key = KeyForItem(item);
      if (Dictionary != null && Dictionary.TryGetValue(key, out var collection)
        && collection.Remove(item))
      {
        if (collection.Count == 0)
          Remove(key);
        return true;
      }
      return false;
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
      foreach (var group in base.Items)
        foreach (var item in group)
          yield return item;
    }

    const string IndexError = "Indexing not supported.";
    public int IndexOf(TElement item) => throw new NotSupportedException(IndexError);
    public void Insert(int index, TElement item) => Add(item);
    public bool Contains(TElement item) => Items.Contains(item);
    public void CopyTo(TElement[] array, int arrayIndex) =>
    throw new NotSupportedException(IndexError);
    new IEnumerable Items => this;
    public bool IsReadOnly => false;
    TElement IList.this[int index]
    {
      get => throw new NotSupportedException(IndexError);
      set => throw new NotSupportedException(IndexError);
    }
  }

  class Grouping : Collection, IGrouping
  {
    public Grouping(TKey key) => Key = key;
    public TKey Key { get; }
  }
}