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

[Andrei Alexandrescu]

On 9/24/12 9:27 AM, Philippe Sigaud wrote:
> On Mon, Sep 24, 2012 at 12:46 PM, Nick Sabalausky
> <SeeWebsiteToContactMe at semitwist.com>  wrote:
>
>> That said, I'm not necessarily opposed to the strict separation if we
>> had a good candidate for built-in tuple literal syntax. But *if* the
>> best we have is parens (and maybe there *is* something better?) then
>> maybe this would be an acceptable way to achieve it?
>
> If the problems in DIP 19 are deemed mostly syntactic (1- and 0-
> element tuples), then maybe *for once* a simple syntax change could
> solve them? I know syntax proposals are a dime a dozen in this
> newsgroup, but why not here, to avoid the ((1)) problem?
>
> For example choosing { 1, 2} to represent a tuple? { } blocks in D
> enclose semi-colon terminated declarations or expressions, but here
> it's enclosing comma-separated expressions. And, since { } is probably
> dangerous without a completly integrated type systems giving a type to
> all expressions (  (){} anyone?) , why not use (| 1, 2 |), or whatever
> syntax strikes our collective fancy? (I propose *not* to use<  ,>)
>
> Then, the compiler has to change the way it prints its internal tuple,
> to follow the new syntax.
>
>> Ie:
>>
>> // (3) is polysemous: Either int or (int)
>> int   a = (3);  // Normal value
>> (int) b = (3);  // One-element tuple
>> auto  c = (3);  // Default to normal "int"?
>
> For the third case, I'd say it defaults to a tuple. But then again,
> using another syntax solves this problem.
>
> auto c  = (| 3 |); // or c = { 3 };

I think my main problem with this is that I'm perfectly happy with the 
baseline, which has "tuple(" as the left delimiter and ")" as the right 
delimiter. I'd be more excited to invent notation if there was 
overwhelming or at least considerable evidence that the notation 
considerably helps certain use cases, or is very frequent. As things 
are, I'd be quite "meh" about suddenly adding lenses.

Andrei