Try this.

void main()
{
    int x = void;
    int y = 3;

    if(y < 10)
        x += 5;
    else
        x = 2;
}

Notice that x is uninitialized, so "x += 5;" shouldn't work.

If you compile this, even with -w, DMD happily accepts it.  But if you throw -O, it gives the error:

dtest.d(187): Error: variable x used before set

This seems to be a relatively recent development, and doesn't seem to be documented.  It's also very surprising that it only happens when -O is thrown.

I like it a lot.  Could this functionality be formalized and extended (i.e. to include accesses to variables declared like "int x;", like it says in the spec)?

On Thu, 09 Apr 2009 18:19:02 +0400, Jarrett Billingsley <jarrett.billingsley@gmail.com> wrote:

> Try this.
>
> void main()
> {
>     int x = void;
>     int y = 3;
>
>     if(y < 10)
>         x += 5;
>     else
>         x = 2;
> }
>
> Notice that x is uninitialized, so "x += 5;" shouldn't work.
>
> If you compile this, even with -w, DMD happily accepts it.  But if you
> throw -O, it gives the error:
>
> dtest.d(187): Error: variable x used before set
>
> This seems to be a relatively recent development, and doesn't seem to
> be documented.  It's also very surprising that it only happens when -O
> is thrown.
>
> I like it a lot.  Could this functionality be formalized and extended
> (i.e. to include accesses to variables declared like "int x;", like it
> says in the spec)?

I believe this is just an optimization and not a general-purpose flow analysis:

Step 0:
int x = void;
int y = 3;

if (y < 10)
   x += 5;
else
   x = 2;

Step 1:
int x = void;
int y = 3;
if (true)
   x += 5;
else
   x = 2;

Step2:
int x = void;
int y = 3;
x += 5;  // Error: variable x used before set

On Thu, Apr 9, 2009 at 10:28 AM, Denis Koroskin <2korden@gmail.com> wrote:

> I believe this is just an optimization and not a general-purpose flow analysis:

It happens even with a non-trivial condition.

On Thu, 09 Apr 2009 18:53:07 +0400, Jarrett Billingsley <jarrett.billingsley@gmail.com> wrote:

> On Thu, Apr 9, 2009 at 10:28 AM, Denis Koroskin <2korden@gmail.com> wrote:
>
>> I believe this is just an optimization and not a general-purpose flow
>> analysis:
>
> It happens even with a non-trivial condition.

Now I am convinced:

extern(C) int rand();

void main()
{
   int x = void;
   if (rand() == 0) {
       x += 5; 		// line 7
   }
}

test.d(7): Error: variable x used before set

It only happens with DMD1.042+

Yay!

"Denis Koroskin" <2korden@gmail.com> wrote in message news:op.ur4kb8ffo7cclz@soldat.creatstudio.intranet...
> Now I am convinced:
>
> extern(C) int rand();
>
> void main()
> {
>    int x = void;
>    if (rand() == 0) {
>        x += 5; // line 7
>    }
> }
>
> test.d(7): Error: variable x used before set
>
> It only happens with DMD1.042+
>
> Yay!

I guess I'm going to have to start using -O in my debug builds...unless this behavior becomes independant of the -O switch...wink wink nudge nudge...

On Thu, 09 Apr 2009 20:36:43 +0400, Nick Sabalausky <a@a.a> wrote:

> "Denis Koroskin" <2korden@gmail.com> wrote in message
> news:op.ur4kb8ffo7cclz@soldat.creatstudio.intranet...
>> Now I am convinced:
>>
>> extern(C) int rand();
>>
>> void main()
>> {
>>    int x = void;
>>    if (rand() == 0) {
>>        x += 5; // line 7
>>    }
>> }
>>
>> test.d(7): Error: variable x used before set
>>
>> It only happens with DMD1.042+
>>
>> Yay!
>
> I guess I'm going to have to start using -O in my debug builds...unless this
> behavior becomes independant of the -O switch...wink wink nudge nudge...
>
>

Yeah, me too!

BTW, that's a breaking change! XD

Denis Koroskin wrote:
> BTW, that's a breaking change! XD

Ssh!