84 lines
3.7 KiB
C#
84 lines
3.7 KiB
C#
// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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// See the LICENSE file in the project root for more information.
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#if NET6_0_OR_GREATER
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using System.Diagnostics.CodeAnalysis;
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#endif
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using System.Reflection;
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using System.Runtime.CompilerServices;
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using System.Threading.Tasks;
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namespace CommunityToolkit.Common;
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/// <summary>
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/// Helpers for working with tasks.
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/// </summary>
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public static class TaskExtensions
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{
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/// <summary>
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/// Gets the result of a <see cref="Task"/> if available, or <see langword="null"/> otherwise.
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/// </summary>
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/// <param name="task">The input <see cref="Task"/> instance to get the result for.</param>
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/// <returns>The result of <paramref name="task"/> if completed successfully, or <see langword="default"/> otherwise.</returns>
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/// <remarks>
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/// This method does not block if <paramref name="task"/> has not completed yet. Furthermore, it is not generic
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/// and uses reflection to access the <see cref="Task{TResult}.Result"/> property and boxes the result if it's
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/// a value type, which adds overhead. It should only be used when using generics is not possible.
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/// </remarks>
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static object? GetResultOrDefault(
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#if NET6_0_OR_GREATER
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[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties)]
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#endif
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this Task task)
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{
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// Check if the instance is a completed Task
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if (
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#if NETSTANDARD2_1
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task.IsCompletedSuccessfully
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#else
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task.Status == TaskStatus.RanToCompletion
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#endif
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)
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{
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// We need an explicit check to ensure the input task is not the cached
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// Task.CompletedTask instance, because that can internally be stored as
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// a Task<T> for some given T (eg. on .NET 6 it's VoidTaskResult), which
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// would cause the following code to return that result instead of null.
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if (task != Task.CompletedTask)
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{
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// Try to get the Task<T>.Result property. This method would've
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// been called anyway after the type checks, but using that to
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// validate the input type saves some additional reflection calls.
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// Furthermore, doing this also makes the method flexible enough to
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// cases whether the input Task<T> is actually an instance of some
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// runtime-specific type that inherits from Task<T>.
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PropertyInfo? propertyInfo = task.GetType().GetProperty(nameof(Task<object>.Result));
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// Return the result, if possible
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return propertyInfo?.GetValue(task);
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}
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}
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return null;
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}
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/// <summary>
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/// Gets the result of a <see cref="Task{TResult}"/> if available, or <see langword="default"/> otherwise.
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/// </summary>
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/// <typeparam name="T">The type of <see cref="Task{TResult}"/> to get the result for.</typeparam>
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/// <param name="task">The input <see cref="Task{TResult}"/> instance to get the result for.</param>
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/// <returns>The result of <paramref name="task"/> if completed successfully, or <see langword="default"/> otherwise.</returns>
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/// <remarks>This method does not block if <paramref name="task"/> has not completed yet.</remarks>
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static T? GetResultOrDefault<T>(this Task<T?> task)
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{
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#if NETSTANDARD2_1
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return task.IsCompletedSuccessfully ? task.Result : default;
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#else
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return task.Status == TaskStatus.RanToCompletion ? task.Result : default;
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#endif
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}
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}
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