DIP1028 - Rationale for accepting as is

[Arine]

On Saturday, 23 May 2020 at 22:38:58 UTC, ag0aep6g wrote:
> On 24.05.20 00:17, Arafel wrote:
>> On 24/5/20 0:02, ag0aep6g wrote:
>>>
>>> ... and @system static constructors and `--boundscheck=off` 
>>> and initializers of globals
>> 
>> Other than `--boundscheck=off`, that is presumably actively 
>> chosen by the user (as is @trust), would the others be allowed 
>> without `@trusted` in otherwise 100% @safe code?
>
> Yup. Today they can be unmarked, defaulting to @system. With 
> DIP 1028, they can be explicitly marked @system. Either way, 
> they don't show up when you only look for "@trusted".
>
>> I would find concerning that any @system code is allowed, but 
>> I guess initializers of globals should be ok as long as they 
>> are @safe themselves?
>
> As long as they're @safe, sure. But they can also be @system.
>
> An example:
> ----
> const int x = 42;
> const int y = 43;
>
> void main() @safe
> {
>     import std.stdio;
>     writeln(x, " ", y); /* Prints "42 43" as expected. */
>     auto px = &x;
>     auto py = &y;
>     writeln(*px, " ", *py); /* Prints "13 14". Wat? */
> }
>
> int* p = cast(int*) &x;
> static this() @system { *p = 13; *++p = 14; }
> ----

That works even if you make the static this() @safe, and remove 
the pointer incrementation.

You'd have to make the p initialization @safe.

     @safe:
         int* p = cast(int*) &x; // error

But note this doesn't work:

     @safe int* p = cast(int*) &x; // compiles

Having the default become @safe will help detect this, as I don't 
imagine that is a whole lot of usage of @safe: to begin with.