Re: In what order static if conditions are evaluated?

[Artur Zawłocki]

On Thursday, 28 March 2013 at 11:50:58 UTC, 1100110 wrote:
On 03/28/2013 06:29 AM, "Artur Zawłocki" 
<artur.zawlo...@gmail.com>" 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


It should behave the "same" as a normal if statement.

Why? static if is not a statement at all, it's a 'conditional 
declaration'. And the order in which declarations are processed 
on the top level is not relevant (unless you have static if's, 
that is), e.g. you can have:

  static if (a)
    static assert (true);

  const bool a = true;

I've just discovered that this is also OK:

  static if (S.a)
    static assert (true);

  struct S { static if if (true) const bool a = true; }