Comma operator = broken design

[Robert Jacques]

On Wed, 07 Dec 2011 13:19:31 -0500, Nick Sabalausky <a at a.a> wrote:

> "Robert Jacques" <sandford at jhu.edu> wrote in message
> news:op.v54q04vd26stm6 at sandford.myhome.westell.com...
>> On Wed, 07 Dec 2011 11:49:33 -0500, Alex Rønne Petersen
>> <xtzgzorex at gmail.com> wrote:
>>>
>>> Why is this operator still kept around?
>>
>> Take your pick:
>> 1) So that legacy B/C/C++/D1/etc code can be trivially ported to D1/D2.
>
> That's a pretty weak counter-argument:
>
> A. I'd think a lot of C/C++ code can't be trivially ported to D anyway.
That statement implies that there is a lot of code that can be trivially ported to D.

> B. "B", seriously? ;)
Yes, the poster was (in part) asking about where the comma operator came from. C did a lot of stupid things to be portable with B and we have all inherited that legacy.

> C. Being able to link to C/C++ makes it less likely to need to port C/C++
> code anyway.
Sure, for code that's in reasonably complete libraries that full fill your use cases and are supported by someone else. That's not always the case.

> D. Outside of for loops (special-case-able), comma operator is rarely used
> in C/C++/D.
Special casing is a big and dangerous hammer. Generally, it introduces extra work for the compiler and cognitive load for the programmer. Now, we have used special casing to detect common errors to great effect, but these don't add cognitive load to the programmer.

> E. Even among actual uses of the comma operator, I think it'd be rare (if
> even possible) to have a use of it that isn't trivially convertable to
> non-comma.
True, but that still implies extra work on the part of the programmer.

>> 2) The comma operator is heavily used in regular old for loops.
>
> That can be special cased.
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?

>> 5) The comma and semicolon are on different keys on US style keyboards.
>> 6) It is trivial to change your keyboard layout (I've hotkeyed Greek for
>> fast math symbols)
>
> Those are very weak counter-arguments.
I don't disagree, but the poster's original argument was (essentially) that EU keyboards put ; and , on the same key, so it was easy to mistype between the two. I was just suggesting that maybe the poster might want to fix their keyboard before trying to 'fix' the language.