小编cod*_*452的帖子

摘自Stephen Cleary关于异步等待的文章:

图2异步无效方法的异常无法通过Catch捕获

private async void ThrowExceptionAsync()
{
  throw new InvalidOperationException();
}
public void AsyncVoidExceptions_CannotBeCaughtByCatch()
{
  try
  {
    ThrowExceptionAsync();
  }
  catch (Exception)
  {
    // The exception is never caught here!
    throw;
  }
}

...异步void方法抛出的任何异常将直接在异步void方法启动时处于活动状态的SynchronizationContext上引发...

这究竟意味着什么？我写了一个扩展示例来尝试收集更多信息.它具有与图2相同的行为:

static void Main()
{

    AppDomain.CurrentDomain.UnhandledException += (sender, ex) => 
    {
        LogCurrentSynchronizationContext("AppDomain.CurrentDomain.UnhandledException");
        LogException("AppDomain.CurrentDomain.UnhandledException", ex.ExceptionObject as Exception);
    };

    try
    {
        try
        {
            void ThrowExceptionVoid() => throw new Exception("ThrowExceptionVoid");

            ThrowExceptionVoid();
        }
        catch (Exception ex)
        {
            LogException("AsyncMain - Catch - ThrowExceptionVoid", ex);
        }

        try
        {
            // CS1998 …

.Returns<T> (this T value, ... )扩展方法如何在引擎盖下工作？

具体来说,如何.Returns根据执行该方法的结果知道它打算配置什么方法？

例:

public interface ICalculator { Add(int a, int b); }

// create mock
var calculator = Substitute.For<ICalculator>();

// How does this piece work under the hood?
calculator.Add(1, 2).Returns(3);