Temporary @trusted scope

[Jonathan M Davis]

On Tuesday, December 18, 2018 5:42:12 AM MST rikki cattermole via 
Digitalmars-d-learn wrote:
> On 19/12/2018 1:34 AM, Per Nordlöw wrote:
> > On Tuesday, 18 December 2018 at 10:42:51 UTC, Jonathan M Davis wrote:
> >> Unfortunately, D does not currently have a way to do that. Only
> >> functions can be marked with @trusted. However, the typical approach
> >> to this problem is to use a lambda, which is more or less
> >> syntactically the same except that it has some extra parens. e.g.
> >>
> >> () @trusted { doUnsafe(); }();
> >
> > Is there a performance hit when using this?
>
> Yes except for ldc with -O3.
> But it is a function not a delegate so it should be all nicely
> prefetched and ready to go. So I wouldn't worry about it too much.

Really? I would have thought that that would be a pretty obvious
optimization (especially if inlining is enabled). I suppose that it doesn't
entirely surprise me if dmd does a poor job of it, but I would have expected
ldc to do better than that. I would think that such an improvement would be
pretty low-hanging fruit for adding to dmd's optimizer though. If not, it
sounds like further justification for adding a feature for this rather than
having to use a lambda. Aside from that though, the lambda trick is simple
enough that it wouldn't surprise me if Walter and Andrei's response to such
a DIP would be to just use the lambda trick.

- Jonathan M Davis