TaskExt.cs

using System;
using System.Threading.Tasks;

namespace KekPuk.Extensions
{
    /// <summary>
    /// Task extension methods
    /// </summary>
    public static class TaskExt
    {
        public static async Task<TOut> AndThen<TIn, TOut>(this Task<TIn> inputTask, Func<TIn, Task<TOut>> mapperFunc)
        {
            if (mapperFunc == null) throw new ArgumentNullException(nameof(mapperFunc));
            return await mapperFunc(await inputTask);
        }

        public static async Task AndThen<TIn>(this Task<TIn> inputTask, Action<TIn> mapperFunc)
        {
            if (mapperFunc == null) throw new ArgumentNullException(nameof(mapperFunc));
            mapperFunc(await inputTask);
        }

        public static async Task<TOut> AndThen<TIn, TOut>(this TIn inputTask, Func<TIn, Task<TOut>> mapperFunc)
        {
            if (mapperFunc == null) throw new ArgumentNullException(nameof(mapperFunc));
            return await mapperFunc(inputTask);
        }
    }
}