DIP 1016 should use expression lowering, not statement lowering

[Andrei Alexandrescu]

On 1/29/19 10:57 AM, Adam D. Ruppe wrote:
> On Tuesday, 29 January 2019 at 15:48:23 UTC, Andrei Alexandrescu wrote:
>> On 1/29/19 10:44 AM, Nicholas Wilson wrote:
>>>   if (auto val = expr(); val) { ... },
>>
>> Since we don't have these constructs, lowering would need to explain 
>> what happens here.
> 
> 
> Nitpick, but D has something very similar to that:
> 
> if(auto val = expr()) { ... }
> 
> it just depends on val implicitly casting to bool.
> 
>> It's okay if the resulting code is ugly, it won't be user-visible.
> 
> We do have to be careful about this - error messages sometimes leak that 
> ugly code out.

Yah, it did happen in the past that implementations have been switched 
from lowering to a dedicated case. Lowerings do remain a terrific tool 
for conveying semantics and DIP authors should not worry about 
implementation details.