On Thursday, 28 March 2013 at 11:52:26 UTC, Don wrote:
On Thursday, 28 March 2013 at 11:29:49 UTC, Artur Zawłocki
wrote:
Hi,
DMD (I'm using v2.060) seems to evaluate conditions in static
if's from top to bottom (at least in a given scope). For
example, consider the following program:
module test;
const bool x = true;
const bool y = true;
struct S {
static assert(y);
static if(x)
static const bool y = false;
static if(y)
static const bool x = false;
}
'x' in the first static if condition refers to .x and the
static if introduces S.y to which 'y' in the second static if
refers. 'y' in the static assert also refers to S.y and thus
the assertion fails:
test.d(8): Error: static assert (y) is false
Now, I guess if the second static if were evaluated first then
'y' in the static assert condition would refer to .y and the
program would compile. Note that dmd evaluates the static
assert *after* both static if's.
So clearly D program semantics depends on the order static
if's and static assert's are evaluated. Are there any standard
rules here (I cannot find anything in Language Reference) or
is this behaviour implementation dependent?
Artur
Yes, it currently evaluates it top to bottom. An algorithm has
been discussed which would remove that restriction; your
example would then compile. It's difficult to implement though.
It has to deal with paradoxes:
static if (!is(typeof(x)) int y = 1;
static if (!is(typeof(y)) int x = 1;
Who wins?
Current already have to deal with paradoxes.
