AsyncLazy.cs

using System;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;

namespace TerrariaPixelArtHelper
{
	/// <summary>
	/// Provides support for asynchronous lazy initialization. This type is fully threadsafe.
	/// </summary>
	/// <remarks>
	/// Comes from http://blog.stephencleary.com/2012/08/asynchronous-lazy-initialization.html
	/// </remarks>
	/// <typeparam name="T">The type of object that is being asynchronously initialized.</typeparam>
	internal sealed class AsyncLazy<T>
	{
		/// <summary>
		/// The underlying lazy task.
		/// </summary>
		readonly Lazy<Task<T>> instance;

		/// <summary>
		/// Initializes a new instance of the <see cref="AsyncLazy{T}"/> class.
		/// </summary>
		/// <param name="factory">The delegate that is invoked on a background thread to produce the value when it is needed.</param>
		public AsyncLazy(Func<T> factory) => this.instance = new Lazy<Task<T>>(() => Task.Run(factory));

		/// <summary>
		/// Initializes a new instance of the <see cref="AsyncLazy{T}"/> class.
		/// </summary>
		/// <param name="factory">The asynchronous delegate that is invoked on a background thread to produce the value when it is needed.</param>
		public AsyncLazy(Func<Task<T>> factory) => this.instance = new Lazy<Task<T>>(() => Task.Run(factory));

		/// <summary>
		/// Asynchronous infrastructure support. This method permits instances of <see cref="AsyncLazy{T}"/> to be await'ed.
		/// </summary>
		public TaskAwaiter<T> GetAwaiter() => this.instance.Value.GetAwaiter();

		/// <summary>
		/// Starts the asynchronous initialization, if it has not already started.
		/// </summary>
		public void Start()
		{
			var unused = this.instance.Value;
		}
	}
}