Discussion Thread: DIP 1035-- at system Variables--Final Review

[Paul Backus]

On Tuesday, 22 February 2022 at 08:47:55 UTC, Stanislav Blinov 
wrote:
> A more pertinent example around file descriptors and memory 
> safety is void-initialization:
>
> ```d
> struct File
> {
>     void write(const(void)[] data) @safe;
>     // ...
>     private int fd;
> }
>
> void main() @safe
> {
>     File f = void; // this compiles in current language, 
> because `File` doesn't have pointers
>     f.write("hello"); // may corrupt memory if 
> (implementation-defined) value of `f.fd` happens to correspond 
> to an existing mapping
> }
> ```

If you attempt to fill in the missing part of your example, I 
think you will find that you cannot actually demonstrate memory 
corruption resulting from `void`-initialization of a file 
descriptor without the use of `@trusted` code (e.g., to cast the 
`void*` returned from `mmap` to some other type of pointer whose 
target type has unsafe values).