Cached Tasks

CachedTasks.cs

// See https://aka.ms/new-console-template for more information
using System.Runtime.CompilerServices;

Console.WriteLine("Program started");

var cache = new Dictionary<string, object>();

//Use lambda, so the task does not start immediately
Func<Task<string>> taskFactory = async () =>
{
    Console.WriteLine("Task started");
    await Task.Delay(1000); // Simulate a delay
    return "Task result";
};

//V1: use CachedTask class
var cachedTask = new CachedTask<string>("key", taskFactory, cache);
Console.WriteLine(await cachedTask);

//V2: use extension method
var cachedTask2 = taskFactory().Cached("key", cache);
Console.WriteLine(await cachedTask2);

public class CachedTask<T>(string key, Func<Task<T>> taskFactory, IDictionary<string, object> cache)
{
    private readonly string _key = key;
    private readonly Func<Task<T>> _taskFactory = taskFactory;
    private readonly IDictionary<string, object> _cache = cache;

    public async Task<T> GetValueAsync()
    {
        if (_cache.TryGetValue(_key, out object? value))
            return (T)value;

        var result = await _taskFactory().ConfigureAwait(false);

        _cache[_key] = result;

        return result;
    }
    
    //Make CachedTask awaitable
    public TaskAwaiter<T> GetAwaiter() => GetValueAsync().GetAwaiter();
}

public static class TaskExtensions
{
    public static Task<T> Cached<T>(this Task<T> task, string key, IDictionary<string, object> cache)
    {
        if (cache.TryGetValue(key, out object? value))
            return Task.FromResult((T)value);

        return task.ContinueWith(t =>
        {
            cache[key] = t.Result;
            return t.Result;
        });
    }
}