for in D versus C and C++

[Denis Koroskin]

On Thu, 19 Mar 2009 20:43:18 +0300, Denis Koroskin <2korden at gmail.com> wrote:

> On Thu, 19 Mar 2009 20:32:54 +0300, Walter Bright  
> <newshound1 at digitalmars.com> wrote:
>
>> BCS wrote:
>>>> Thu, 19 Mar 2009 06:35:37 -0400, Steve Teale wrote:
>>>>
>>>>> for (; a<b; a++);
>>>>>
>>>>> is illegal in D.
>>>>>
>>>>> Doesn't this break a lot of C and C++ code?
>>>>>
>>>> for (; a<b; a++) {}
>>>>
>>>> is legal.  I don't think that an empty statement after for is used in
>>>> "a lot of code."
>>>>
>>>  it's a trivial fix and easy to find. Heck, you hardly need to think!
>>
>> No, it isn't easy to find. This is in D because a colleague of mine,  
>> who was an expert C programmer (the best in the company I was working  
>> for), came to me with:
>>
>> for (xxx; i < 10; i++);
>> {
>>       ... code ...
>> }
>>
>> and said he could not figure out why his loop executed only and exactly  
>> once. He'd fiddled with it for a whole afternoon. He said he must be  
>> missing something obvious. I said you've got an extra ; after the ). He  
>> smacked his head and about fell over backwards.
>>
>> So it's illegal in D, along with:
>>
>>     if (condition);
>>
>> and similar constructs. Have to use a { } to indicate a blank statement.
>
> Funny enough, or programming department chief posted the following  
> question in our corporate newsgroup:
>
> Why the hell this function enters infinite loop?
>
> void treeWalkWithoutRecursion( Node* head )
> {
>     Stack   s;
>     s.push( head );
>     while ( !s.empty() );
>     {
>         Node* tmp = s.pop();
>         if ( !tmp->marked )
>         {
>             if ( tmp->right  )
>                 s.push( tmp->right );
>             s.push( tmp );
>             if ( tmp->left )
>                 s.push( tmp->left );
>             tmp->marked = true;
>         }
>         else
>             doSomeThing( tmp );
>     }
> }

That was less than a week ago. I'd say that this type of bugs will live as long as C++ lives.