DotNext by Roman Sakno

<PackageReference Include="DotNext" Version="1.2.6" />

.NET API 245,248 bytes

 CompletedTask<T, C>

public static class CompletedTask<T, C> where C : Constant<T>
Represents cache of completed tasks.
public static readonly Task<T> Task

Represents the completed task containing a value passed as constant through C generic parameter.