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

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?

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.

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.

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;
	}
}

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

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.

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.

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

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.