`in` parameters made useful

[Mathias LANG]

On Tuesday, 25 August 2020 at 12:09:45 UTC, Kagamin wrote:
>
> The backend doesn't know how to load the data. It matters to 
> the programmer, because it affects performance.
>
> Another example:
> void log(in ref int n)
> {
>   write(fd, &n, n.sizeof);
> }
> If the argument here is passed by value, it will need to fiddle 
> with stack and the code will be less optimal.

I assume you imply that it's less optimal because it's taking the 
address of it ?


> If a non-POD object is passed by value, it will have extra 
> calls to postblit and destructor.

https://github.com/dlang/dmd/blob/master/changelog/preview-in.dd

> - If the type has an elaborate copy or destruction (postblit, 
> copy constructor, destructor),
> the type is always passed by reference.