CachedSelect

.CachedSelect<,>(selector, equalityComparer?) is similar to .Select<,>, however it caches values and returns same value reference on every iteration.

// Car id source
List<string> keys = new List<string> { "XYZ-123", "ABC-789" };
// Car enumerable (constructs cars from id)
IEnumerable<Car> cars = keys.CachedSelect<string, Car>(id => new Car { Id = id });

// Get reference to first car
Car car0 = cars.First();

// Print cars
foreach (Car car in cars)
    Console.WriteLine(car);
// Car { Id = XYZ-123, Name =  }
// Car { Id = ABC-789, Name =  }

// Remove second car
keys.RemoveAt(1);

// Print cars
foreach (Car car in cars)
    Console.WriteLine(car);
// Car { Id = XYZ-123, Name =  }

// Get reference to first car
Car car0x = cars.First();

// Enumerable still returns same reference
Console.WriteLine(object.ReferenceEquals(car0, car0x)); // True

// Dispose cache
((IDisposable)cars).Dispose();
// Disposed ABC-789
// Disposed XYZ-123

public record Car : IDisposable
{
    public string Id { get; set; } = "id";
    public string Name { get; set; } = "";

    public void Dispose() => Console.WriteLine($"Disposed {Id}");
}

Full Example

Full example

using System;
using System.Collections.Generic;
using System.Linq;
using Avalanche.Utilities;

public class cachedselect
{
    public static void Run()
    {
        {
            // <01>
            // Car id source
            List<string> keys = new List<string> { "XYZ-123", "ABC-789" };
            // Car enumerable (constructs cars from id)
            IEnumerable<Car> cars = keys.CachedSelect<string, Car>(id => new Car { Id = id });

            // Get reference to first car
            Car car0 = cars.First();

            // Print cars
            foreach (Car car in cars)
                Console.WriteLine(car);
            // Car { Id = XYZ-123, Name =  }
            // Car { Id = ABC-789, Name =  }

            // Remove second car
            keys.RemoveAt(1);

            // Print cars
            foreach (Car car in cars)
                Console.WriteLine(car);
            // Car { Id = XYZ-123, Name =  }

            // Get reference to first car
            Car car0x = cars.First();

            // Enumerable still returns same reference
            Console.WriteLine(object.ReferenceEquals(car0, car0x)); // True

            // Dispose cache
            ((IDisposable)cars).Dispose();
            // Disposed ABC-789
            // Disposed XYZ-123
            // </01>
        }
    }

    // <05>
    public record Car : IDisposable
    {
        public string Id { get; set; } = "id";
        public string Name { get; set; } = "";

        public void Dispose() => Console.WriteLine($"Disposed {Id}");
    }
    // </05>
}