Cannot convert type ‘Task’ to ‘Task’

by

C# does not allow variance on classes, only interfaces and delegates that are parameterized with reference types. Task<T> is a class.

This is somewhat unfortunate, as Task<T> is one of those rare classes that could be made safely covariant.

However it is easy enough to convert a Task<Derived> to a Task<Base>. Just make a helper method / lambda that takes a Task<Derived> and returns Task<Base>, await the passed-in task, and return the value cast to Base. The C# compiler will take care of the rest. Of course you lose referential identity, but you weren’t ever going to get that with a class.

More Related Contents:

  1. linq syntax: What is the type that this returns? How can I now go ahead and use firstRow.ingredientName etc?
  2. Inconsistent Accessibility: Parameter type is less accessible than method
  3. Referencing a variable from another method
  4. No overflow exception for int in C#?
  5. Playing a MP3 file in a WinForm application
  6. WPF: Binding a ContextMenu to an MVVM Command
  7. Does C++11 have C#-style properties?
  8. Listen to changes of dependency property
  9. “Could not load type [Namespace].Global” causing me grief
  10. Zoom and translate an Image from the mouse location
  11. single app.config multi-project c#
  12. How to implement GZip compression in ASP.NET?
  13. How do I display the DisplayAttribute.Description attribute value?
  14. Parallel Sort Algorithm
  15. How to asynchronously read the standard output stream and standard error stream at once
  16. Unzipping a .gz file using C#
  17. Password encryption/decryption code in .NET
  18. C# SHA-1 vs. PHP SHA-1…Different Results?
  19. Get the SourceControl of a DropDownMenu
  20. c#: difference between “System.Object” and “object”
  21. Inheriting comments from an interface in an implementing class?
  22. C# Threading/Async: Running a task in the background while UI is interactable
  23. Control.AddRange(…) is slow
  24. big issue in converting string to datetime using linq-to-entities
  25. Named Pipe Server throws UnauthorizedAccessException when creating a second instance if PipeSecurity is set
  26. How do I transform appsettings.json in a .NET Core MVC project?
  27. Why does my C# client, POSTing to my WCF REST service, return (400) Bad Request?
  28. RichTextBox Newline Conversion?
  29. Best way to iterate folders and subfolders
  30. Run a method before all methods of a class

Leave a Comment