C bitfields guarantees

[Timon Gehr]

On 7/9/24 02:29, Walter Bright wrote:
> 
> Let's say Bob (poor Bob) needs to convert 20,000 lines of C code to D. I 
> know you've done some of this yourself! Bob doesn't want to go through 
> it line by line. Isn't it nice for Bob if it "just works"?

It won't, some edits will be necessary.

> If all those 
> data declarations just work? Especially if the result still has to be 
> compatible with the files that C code wrote out?
> 
> But what if the compiler says "Bob, you can't lay out a bitfield like 
> that!"

The compiler should simply say: "Bob, are you sure you want to lay out a 
bitfield like this?" If Bob is comfortable with it, he can add 
`extern(C)` and move on.

> Or worse, it lays out the bitfield into a portable (but 
> different) layout.

Well I think this is not an option.

> Then it doesn't just work, Bob has got some debugging 
> to do (while Bob curses D and me), and Bob's got to figure out an 
> alternative. Who wants to do that? Not Bob. Not me. Not nobody not nohow.

As far as I am concerned, this is an irrelevant straw man. I don't want 
this. I never suggested anything that would cause this. It's pure FUD.

Similarly, I don't want to go chasing down subtle differences in 
behavior/cache performance etc. between platforms. Portability may be 
important. It shouldn't be insane by default, it should be insane by 
choice. Informed consent.

Especially given that bitfields have a "much nicer syntax" than 
alternative approaches. It's not nice to hand out a footgun disguised as 
candy.