Comma operator = broken design

[Alex Rønne Petersen]

On 10-12-2011 02:39, Jonathan M Davis wrote:
> On Friday, December 09, 2011 20:18:36 Robert Jacques wrote:
>> On Fri, 09 Dec 2011 01:20:45 -0500, Kagamin<spam at here.lot>  wrote:
>>> On Thursday, 8 December 2011 at 17:18:57 UTC, Joshua Reusch wrote:
>>>>> Ahem. So are you suggesting that (a,b) means a tuple
>>>>> everywhere but in a
>>>>> for loop, where it is used to separate two statements?
>>>>
>>>> If we use the comma operator only for tuples, there needn't to
>>>> be a special case for loops:
>>>>
>>>> for(x, y = 0 , 100; x<  y ; x, y += 1,-1) { ... }
>>>
>>> for(int x, y = 0 , 100; x<  y ; x, y += 1,-1) { ... }
>>>
>>> ?
>>
>> Here's how I understood it:
>>
>> int x,y; // Defined somewhere in the code above
>>
>> for( (x,y) = (0,100); x<  y ; (x,y) += (1,-1) ) { ... }
>>
>> So you have variable capture, assignment and add-assign happening.
>
> I'd _hate_ to be restricted to doing the same operation in the 3rd portion of
> a for loop for all of its parts. The comma operator is _perfect_ for there,
> and I wouldn't want to see its behavior changed there regardless. e.g. things
> like this should continue to be perfectly possible and legal
>
> for(; cond; ++x, y *= 2) {}
>
> Tuples do _not_ have the proper semantics for a for loop. It would be one
> thing for the comma operator were to go away in the general case, but it would
> be horrible IMHO for its behavior to be changed in for loops - be it in an
> effort to make it act like it's using tuples or any other reason.
>
> - Jonathan M Davis

Indeed, having the comma operator in for loops is perfectly normal; even 
C# has this.

- Alex