Release D 2.094.0

[Steven Schveighoffer]

On 10/1/20 10:36 AM, Meta wrote:
> On Thursday, 1 October 2020 at 09:49:36 UTC, Mathias LANG wrote:
>> Author here. The most complete way to know would be to read the 
>> changelog: https://dlang.org/changelog/2.094.0.html#preview-in
>> The TL;DR is that, in addition to `const scope`, `in` now 
>> automatically behaves as `ref` when "it makes sense" such as large 
>> value types or presence of destructors / postblit (more details in the 
>> changelog!) and will accept rvalues, unlike other ref parameters.
> 
> Why was this added when we already have `auto ref`? Yes, it makes the 
> function a template, but if `in` can automatically choose whether the 
> variable is ref or not, then auto ref could easily do the same.

There is a difference. `in` is choosing it based on the type, not 
whether it's an rvalue or lvalue. auto ref doesn't care whether it's an 
int or a 1k-sized struct, if it's an lvalue, it's ref, and if it's an 
rvalue, it's non-ref.

Not only that, but every auto-ref parameter is another template 
parameter varying on the usage. So calling on an lvalue and rvalue will 
generate 2 separate mostly-identical functions.

With -preview=in, only one function is generated per type.

-Steve