Integer promotion issue

[Adam D. Ruppe]

On Sunday, 26 January 2020 at 13:01:58 UTC, Guillaume Piolat 
wrote:
> It seems silly however in the wild this C int promotion rule 
> make stuff work without the author knowledge.

indeed.

Though if that rule wasn't there we'd probably have more author 
knowledge anyway. But it is too late now.

For D though maybe we could change our truncating rule to make it 
more relaxed if all the inputs are literals or the same type as 
the assignment. So it still promotes, just allows implicit cast 
back to the original.

short a;
short b = a + 1; // implicitly does cast(short)(cast(int) a + 1)

int a;
short b;
short c = b + a; // error: cannot implicitly cast because the 
`int a` triggers more strictness

ubyte a;
ubyte b;
ubyte c = a + b; // allowed

ushort d;
ubyte c = a + d; // prohibited



So it will follow the C promotion rules and then implicitly cast 
back to the largest integral type in the original expression.

ubyte a = 255 + 5; // literals are excluded from the new implicit 
rule loosening, so this does what it does now = int(int(255) + 
int(5)) => VRP -> too large for ubyte, error.


Cuz I just think if we are explicitly specifying a particular 
smaller type throughout it indicates a pretty clear intent 
already.