Why isn't field-wise constructor automatic for structs and not classes?

[John Colvin via Digitalmars-d-learn]

On Saturday, 2 January 2016 at 02:12:19 UTC, Shriramana Sharma 
wrote:
> If I have:
>
> struct TimeSpan { double start, end; }
>
> Then both the following automatically work:
>
> auto s = TimeSpan();
> auto t = TimeSpan(1, 2);
>
> But if I make it a class (I need to) then I have to explicitly 
> define a field-wise constructor else only a constructor with no 
> args is automatically defined. Why can't the field-wise 
> functionality be automatic for classes too?

Strictly speaking you aren't calling a constructor there, you're 
writing a struct literal.