I've been experimenting with the -betterC switch and stumbled upon something that didn't quite make sense to me.

I've put together a small example [1] of Win32 code with a window callback that has to be nothrow as per the definition of WNDPROC somewhere in core.sys.windows. However, calling anything from within the window callback not marked as nothrow will result in a compile error. This behavior is expected for regular D code and there are many ways to fix the code so the compiler no longer emits the error. What bugs me is the following.

According to the docs, exceptions "won't work":

From https://dlang.org/spec/betterc.html#consequences
> As no Druntime is available, many D features won't work. For example:
> [...]
>     7. Exceptions
> [...]

To me, this means it should be impossible to write -betterC code that throws exceptions. So shouldn't -betterC imply nothrow on all functions by default? Is this a compiler bug? If not, in what way is the explicit nothrow attribute still useful for -betterC?


[1] https://gist.github.com/Manuzor/81cc01d57543202d68eab5a84d944027

On Sunday, 3 December 2017 at 15:24:27 UTC, Manuel Maier wrote:
> I've been experimenting with the -betterC switch and stumbled upon something that didn't quite make sense to me.

betterC doesn't change the language, it just doesn't compile in all the features automatically. So rules about nothrow etc. decorations are still in place, even if the feature isn't actually available at this time. The same code you build with -betterC can almost always be built without the switch too, and continue to work the same way.

> According to the docs, exceptions "won't work":

That may be a temporary restriction. It is already possible to do exceptions with -betterC code if you link in the functions yourself (notably, betterC modules are permitted to be used in a regular druntime based application), and in the future, such may be done automatically on demand too.

Thanks Adam, that cleared it up for me.