public static async Task<Dictionary<K, V>> ToDictionaryAsync<T, K, V>(this ChannelReader<T> source,
                                                                           Func<T, K> key,
                                                                           Func<T, V> value,
                                                                           IEqualityComparer<K> comparer,
                                                                           ChannelParallelOptions options)

using Amphisbaena;
using Amphisbaena.Linq;

...

int[] data = new int[] {1, 2, 3, 4, 5, 6, 7, 8, 9};

var dict = await data
  .ToChannelReader()
  .ToDictionaryAsync(item => item, 
                     item => item * item);