Temporary @trusted scope

[H. S. Teoh]

On Tue, Dec 18, 2018 at 08:52:29AM -0500, Steven Schveighoffer via Digitalmars-d-learn wrote:
> On 12/18/18 6:29 AM, Simen Kjærås wrote:
> > On Tuesday, 18 December 2018 at 10:14:50 UTC, Per Nordlöw wrote:
> > > What's the preferred way of creating a temporary @trusted scope
> > > without writing a separate  function?
> > 
> > Jonathan's idea might also be encapsulated in a function, just like
> > assumeUnique in Phobos:
> > 
> > import std.stdio;
> > 
> > template unsafe(alias fn) {
> >      @trusted auto unsafe(T...)(T args) {
> >          return fn(args);
> >      }
> > }
> > 
> > @system void fun(int n) {
> >      writeln("foo!");
> > }
> > 
> > @safe unittest {
> >      unsafe!({
> >          fun(2);
> >      });
> > 
> >      unsafe!fun(2);
> > }
> 
> Wow, I really like this. The only real problem is that one generally
> searches for @trusted when looking for unsafe code, but unsafe is
> pretty obvious too. Also, args should be auto ref.
> 
> Only thing better I can think of (for the second example) is to define
> a prototype with the correct information, only with @trusted (and
> specify the mangle). But any decent compiler should get rid of any
> overhead there.
[...]

I'm not so sure I like this. @trusted bits of code really should have a
safe API that cannot be called in a way that breaks @safe. Being able to
essentially "cast away" @safe for arbitrary bits of code seems to me to
be a rather scary, underhanded way of undermining @safe.

OTOH, if your function is very large and only isolated bits are
non- at safe, then a construct like this one could help, by making the code
less noisy, and ensuring that the other parts of the code still remain
@safe. (Though IMO in such cases the function may be better refactored
to encapsulate away the @trusted bits in functions with safe APIs, and
keep the @safe code all in one place.)


T

-- 
MASM = Mana Ada Sistem, Man!