DIP19: Remove comma operator from D and provision better syntactic support for tuples

[bearophile]

Timon Gehr:

> Switch is syntax sugar for jump tables. An adequate pattern 
> matching
> construct would not require explicit control flow statements, 
> and it would be an expression of arbitrary type.

Introducing a good pattern matching syntax in D requires the 
introduction of a good amount of complexity. This idea was 
discussed few times in past.

D switches also work on strings, wstrings, dstrings, so the idea 
of extending them to work on small array is not too much 
different.

I think that switching on structs, and tuples with 
auto-assignment of variables for tuple fields, is enough to 
extend the usefulness of D switches significantly, while it 
introduces no new keywords, and not a lot of complexity for both 
the compiler and the programmer that has to learn D language.

Bye,
bearophile