ImportC const

Jul 09, 2022

Steven Schveighoffer

Jul 09, 2022

Dave P.

Jul 09, 2022

Jul 11, 2022

Jul 11, 2022

Jul 11, 2022

Jul 10, 2022

Brian Callahan has a blog post about ImportC:

https://briancallahan.net/blog/20220704.html

One part identifies a current design choice that breaks C code:

OK, so I built this file with clang and kept going. There was one more file that DMD couldn't compile:

dmd -g -O -P=-DEMACS -P=-DVI -ofexpr.o -c expr.c
expr.c(204): Error: cannot modify `const` expression `(*es).tok`
expr.c(205): Error: cannot modify `const` expression `(*es).val`

I wonder if this is a bug in ImportC. No other C compiler we've tried fails on this code.

The answer is, no it's not a bug, it's by design: https://dlang.org/spec/importc.html#const

Is there any benefit to breaking any usage of const in C when trying to compile C code?

-Steve

July 09, 2022

Re: ImportC const

Posted by Dave P.
in reply to Steven Schveighoffer

Permalink

Dave P.

Posted in reply to Steven Schveighoffer

Permalink

On Saturday, 9 July 2022 at 17:07:16 UTC, Steven Schveighoffer wrote:

Brian Callahan has a blog post about ImportC:

https://briancallahan.net/blog/20220704.html

One part identifies a current design choice that breaks C code:

OK, so I built this file with clang and kept going. There was one more file that DMD couldn't compile:

dmd -g -O -P=-DEMACS -P=-DVI -ofexpr.o -c expr.c
expr.c(204): Error: cannot modify `const` expression `(*es).tok`
expr.c(205): Error: cannot modify `const` expression `(*es).val`

I wonder if this is a bug in ImportC. No other C compiler we've tried fails on this code.

The answer is, no it's not a bug, it's by design: https://dlang.org/spec/importc.html#const

Is there any benefit to breaking any usage of const in C when trying to compile C code?

-Steve

I reported this as a bug a while ago: https://issues.dlang.org/show_bug.cgi?id=22759

IMO we should ignore const in this case as presumably the code has already compiled with a different C compiler.

On 7/9/22 19:07, Steven Schveighoffer wrote: > Brian Callahan has a blog post about ImportC: > > https://briancallahan.net/blog/20220704.html > > One part identifies a current design choice that breaks C code: > > OK, so I built this file with clang and kept going. There was one more file that DMD couldn't compile: > > ``` > dmd -g -O -P=-DEMACS -P=-DVI -ofexpr.o -c expr.c > expr.c(204): Error: cannot modify `const` expression `(*es).tok` > expr.c(205): Error: cannot modify `const` expression `(*es).val` > ``` > I wonder if this is a bug in ImportC. No other C compiler we've tried fails on this code. > > The answer is, no it's not a bug, it's by design: https://dlang.org/spec/importc.html#const > > Is there any benefit to breaking any usage of const in C when trying to compile C code? > > -Steve It's a "limitation": https://dlang.org/spec/importc.html#limitations I guess the underlying issue is that type qualifiers and their combinations are implemented as bitfields in DMD, so adding new ones is pretty hard.

On Monday, 11 July 2022 at 04:27:29 UTC, Walter Bright wrote: > On 7/9/2022 10:16 AM, Max Samukha wrote: >> If importing C fails, ImportC is useless, obviously. > > So true. I shall have myself flogged forthwith. Please stream it live!

On Monday, 11 July 2022 at 07:09:50 UTC, Max Samukha wrote: > On Monday, 11 July 2022 at 04:27:29 UTC, Walter Bright wrote: >> On 7/9/2022 10:16 AM, Max Samukha wrote: >>> If importing C fails, ImportC is useless, obviously. >> >> So true. I shall have myself flogged forthwith. > > Please stream it live! Beerconf is getting out of control.

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