Re: do-while loops
On 12/28/2011 10:45 PM, Manfred Nowak wrote:
bearophile wrote:
void main() {
do {
int x = 5;
} while (x != 5); // Error: undefined identifier x
}
Do you mean, that the similar while-loop should also be okay?
| void main() {
| while (x != 5) /* uses `x' out of _following_ scope */ {
| int x = 5;
| };
| }
-manfred
No, it is not any more valid than the following code, even if condition
and body are scoped together:
void main() {
bool _ = x != 5;
int x = 5;
}
Related:
https://github.com/D-Programming-Language/dmd/pull/342#issuecomment-3232150
Re: do-while loops
bearophile wrote:
> void main() {
> do {
> int x = 5;
> } while (x != 5); // Error: undefined identifier x
> }
>
Do you mean, that the similar while-loop should also be okay?
| void main() {
| while (x != 5) /* uses `x' out of _following_ scope */ {
| int x = 5;
| };
| }
-manfred
Re: do-while loops
On Wednesday, December 28, 2011 21:37:56 Timon Gehr wrote:
> Well, do loops are the least frequently used looping constructs. Also,
> if you actually have code like the following
>
> import foo; // defines global symbol 'x'
>
> void main(){
> do {
> int x;
> // ...
> }while(x<2);
> }
>
>
> It is likely that it is actually buggy because the programmer assumed
> lookup would work differently.
I don't know whether the change is worth making or not (it arguably does
introduce an inconsistency into the scoping rules - though it _would_
definitely be useful), but I wouldn't really expect it to break any code. And
I'd have to concurr that if it did, odds are that the code was buggy anyway.
- Jonathan M Davis
Re: do-while loops
On 12/28/2011 09:32 PM, Alex Rønne Petersen wrote:
On 28-12-2011 18:50, Timon Gehr wrote:
On 12/28/2011 06:42 PM, bearophile wrote:
Timon Gehr:
I fully agree, but why does this go to D.learn?
Because I think there's no hope to see this situation changed :-)
Bye,
bearophile
Why? The only D code that would get broken would be code that uses a
global variable in the loop condition of the same name as a do loop
local variable.
That's still a bit of a risk to take for such a small change, IMHO.
- Alex
Well, do loops are the least frequently used looping constructs. Also,
if you actually have code like the following
import foo; // defines global symbol 'x'
void main(){
do {
int x;
// ...
}while(x<2);
}
It is likely that it is actually buggy because the programmer assumed
lookup would work differently.
Re: do-while loops
On 28-12-2011 18:50, Timon Gehr wrote: On 12/28/2011 06:42 PM, bearophile wrote: Timon Gehr: I fully agree, but why does this go to D.learn? Because I think there's no hope to see this situation changed :-) Bye, bearophile Why? The only D code that would get broken would be code that uses a global variable in the loop condition of the same name as a do loop local variable. That's still a bit of a risk to take for such a small change, IMHO. - Alex
Re: do-while loops
28.12.2011 16:29, bearophile пишет:
One thing that I often find not handy in the design of do-while loops: the scope of their
body ends before the "while":
void main() {
do {
int x = 5;
} while (x != 5); // Error: undefined identifier x
}
So I can't define inside them variables that I test in the while().
This keeps the scope clean, but it's not nice looking:
void main() {
{
int x;
do {
x = 5;
} while (x != 5);
}
}
Bye,
bearophile
+1
I faced it a few days ago too. An enhancement request should be filled.
Even if it will be resolved as WONTFIX, at least we will know a reason.
Re: do-while loops
On 12/28/2011 06:42 PM, bearophile wrote: Timon Gehr: I fully agree, but why does this go to D.learn? Because I think there's no hope to see this situation changed :-) Bye, bearophile Why? The only D code that would get broken would be code that uses a global variable in the loop condition of the same name as a do loop local variable.
Re: do-while loops
Timon Gehr: > I fully agree, but why does this go to D.learn? Because I think there's no hope to see this situation changed :-) Bye, bearophile
Re: do-while loops
On 12/28/2011 8:29 AM, bearophile wrote:
One thing that I often find not handy in the design of do-while loops: the scope of their
body ends before the "while":
void main() {
do {
int x = 5;
} while (x != 5); // Error: undefined identifier x
}
I would just rewrite it like so:
void main(){
while(true){
int x = 5;
if(x != 5) continue;
break;
}
}
Re: do-while loops
On 12/28/2011 04:01 PM, Andrej Mitrovic wrote:
A very small cheat:
void main()
{
if (int x = 0)
do {
x = 5;
} while (x != 5);
}
Only works for this simple case though. Put your post in d.general, I
totally agree with it as well.
This won't work. The 'if' condition is always false.
Re: do-while loops
A very small cheat:
void main()
{
if (int x = 0)
do {
x = 5;
} while (x != 5);
}
Only works for this simple case though. Put your post in d.general, I
totally agree with it as well.
Re: do-while loops
On 12/28/2011 02:29 PM, bearophile wrote:
One thing that I often find not handy in the design of do-while loops: the scope of their
body ends before the "while":
void main() {
do {
int x = 5;
} while (x != 5); // Error: undefined identifier x
}
So I can't define inside them variables that I test in the while().
This keeps the scope clean, but it's not nice looking:
void main() {
{
int x;
do {
x = 5;
} while (x != 5);
}
}
Bye,
bearophile
I fully agree, but why does this go to D.learn?
do-while loops
One thing that I often find not handy in the design of do-while loops: the
scope of their body ends before the "while":
void main() {
do {
int x = 5;
} while (x != 5); // Error: undefined identifier x
}
So I can't define inside them variables that I test in the while().
This keeps the scope clean, but it's not nice looking:
void main() {
{
int x;
do {
x = 5;
} while (x != 5);
}
}
Bye,
bearophile
