Comma expression as tuple operator [was Tuples, C#, Java, language

[Denis Koroskin]

On Wed, 30 Dec 2009 09:29:22 +0300, Don <nospam at nospam.com> wrote:

> justme wrote:
>> grauzone Wrote:
>>
>>> BCS wrote:
>>>> Hello justme,
>>>>
>>>>> bearophile Wrote:
>>>>>
>>>>>> C# will probably not follow the route of stagnation of Java for some
>>>>>> more time, thanks to Mono too. I don't like that string  
>>>>>> interpolation
>>>>>> syntax because it looks unsafe, and that design of tuples can be
>>>>>> improved, but they are listening to programmes (even if they risk
>>>>>> creating a mudball language):
>>>>>>
>>>>>> http://www.infoq.com/news/2009/12/Mono-CSharp-Ex
>>>>>>
>>>>>> More on those tuples:
>>>>>> http://tirania.org/blog/archive/2009/Dec-23.html
>>>>>> Eventually it will be quite useful to have some very well designed
>>>>>> multi-return support in D (like those tuples, but better).
>>>>>>
>>>>> Doesn't D2 already have tuples in Phobos. D has the comma operator
>>>>> which C# doesn't so such syntax is not possible in D, me thinks.
>>>>>
>>>> A though on the comma operator: if the comma operator were defined to  
>>>> give a tuple type and be implicitly castable to any suffix of it's  
>>>> self, then you could get both the comma expression usage that Walter  
>>>> wants as well as all the fun things that tuple expressions give.
>>>>
>>>> int i = 1, j = 2;
>>>>
>>>> (i, j) = (j, i); // swap
>>>>
>>>> i = (j+= i, i*2 + j); // first expression gets evaluated and dropped.
>>>>
>>>> Thoughts?
>>> Why not make the programmer write tuple[$-1] instead?
>>>
>>> i = (j += i, i*2 + j)[$-1];
>>>
>>> There's no reason to keep the current comma operator.
>>  It's his language, after all. I'm sure there is a good reason why the  
>> old C style comma expression is still there. Maybe it's good for  
>> generating parsers with some software tools?
>
> I doubt it. The thing is, in Walter's world (which I've been living in  
> for the fast six months), comma is really important. It's used  
> everywhere inside the compiler. Interestingly, however, the compiler's  
> comma operator is not the same as the one in D! In the compiler internal  
> comma, you can have declarations:
>
> int x = (int y=foo(); y*y);
>
> And also, the compiler can generate unique variable names, which makes  
> it much more useful: it's basically a way to generate a simple function  
> which is guaranteed to be inlined.
> So I think, that Walter's opinion is based on strong personal  
> experience; but I don't think that experience is actually relevant.

I believe he could replace comma operator with AOC (Any Other Character)  
operator: just replace comma with "something" which is not yet used.  
Choose some fancy-looking Unicode character that no one will really use  
but the compiler itself to generate intermediate code.