Am 09.02.2017 um 18:00 schrieb Kagamin:
On Wednesday, 8 February 2017 at 15:18:34 UTC, Sönke Ludwig wrote:
The problem is that there are two affected call stacks - the @system
API function that registers the @system callback, wrapping/casting it
as @trusted, and the event handler that later on actually calls the
callback. The latter place is where the hidden violation of the @safe
guarantees happens.

Hidden from whom? Since it's user, who supplies @system code to vibe, he
knows that the resulting program doesn't provide @safe guarantees.
It can be communicated at the API level:

int f(@safe void delegate() dg) @safe
{ code }
int f(@system void delegate() dg) @system
{ return f(cast(@safe void delegate())dg); }

So that unsafe overload would be only callable from unsafe code.

Hidden from the code that calls the callback. This may be an acceptable trade off in this particular case, because this is crossing a library border, but in general this is just misuse of the safety system, since the effects of the cast leave the scope of @system/@trusted.

I don't know, I don't really like this, but maybe I should just postpone the `deprecated` attribute to be added for 0.8.1 to leave more room for a final decision.

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