DIP 1009--Improve Contract Usability--Preliminary Review Round 1

[Moritz Maxeiner via Digitalmars-d]

On Sunday, 25 June 2017 at 15:46:12 UTC, Petar Kirov [ZombineDev] 
wrote:
>
> out result => result > 0 // not much worse
>
> out __result > 0 // even better (__result works at least since 
> [0])
>
> I suggested adding a shorter / better looking contextual 
> keyword -
> `result` - a while ago [1]:
> ---
> out result > 0 // perhaps the best
> ---

I have no stance with having to specify a result identifier, or 
using __result, making `result` special, *but*: Not requiring 
parentheses here introduces an unacceptable language 
inconsistency:

auto x(T)(T t)
   if (...)
   in (...)
   out ...
{
     ...
}

If you also propose to drop the parentheses for `in`, that still 
leaves the inconsistency with `if`, i.e. now `if` must be changed 
to also drop the parentheses in template constraints. That, 
however, leads then to an inconsistency between different uses of 
`if` and thus all other occurrences of `if` in the grammar must 
now be made to work without parenthesis. This then leads to even 
more inconsistencies with `for`, `while`, etc. that now also will 
have to be changed.

>
> I'm wondering if `out result > 0` (or if not `out __result > 0`)
> would be too much of a stretch for the language grammar.
>

As argued above, it would essentially require making all uses of 
parenthesis for conditions optional or introduce atrocious 
inconsistencies.
If this is to be done, I believe it belongs in a separate DIP 
"Optional parenthesis for conditions", while this DIP uses 
parentheses.