-preview=safer for D

[Paul Backus]

On Saturday, 14 December 2024 at 08:46:35 UTC, Walter Bright 
wrote:
> Now that this has been merged into master, what are your 
> reactions?

I agree with Jonathan M Davis that the behavior of this flag 
should never be made the default.

As I said in my response to the initial proposal [1], it has all 
of the costs of @safe-by-default (breaks lots of existing code) 
without any of the benefits (reducing attribute spam and 
ecosystem fragmentation). It does nothing to help D programmers 
who are already using @safe, and creates a new source of 
annoyance for people who are currently happy with @system as the 
default.

The easiest way to satisfy the compiler when -preview=safer is 
enabled is to mark all the functions it flags as explicitly 
@system. Because of this, I think it's unlikely that 
-preview=safer will achieve its stated goal of "mov[ing] such 
code to @safe" [2].

[1] 
https://forum.dlang.org/post/dkbrgvjcqsdpuvaeckty@forum.dlang.org
[2] 
https://github.com/WalterBright/documents/blob/38f0a846726b571f8108f6e63e5e217b91421c86/safer.md#rationale