safety model in D

[dsimcha]

== Quote from Andrei Alexandrescu (SeeWebsiteForEmail at erdani.org)'s article
> SafeD is, unfortunately, not finished at the moment. I want to leave in
> place a stub that won't lock our options. Here's what we currently have:
> module(system) calvin;
> This means calvin can do unsafe things.
> module(safe) susie;
> This means susie commits to extra checks and therefore only a subset of D.
> module hobbes;
> This means hobbes abides to whatever the default safety setting is.
> The default safety setting is up to the compiler. In dmd by default it
> is "system", and can be overridden with "-safe".
> Sketch of the safe rules:
> \begin{itemize*}
> \item No @cast@ from a pointer type to an integral type and vice versa
> \item No @cast@ between unrelated pointer types
> \item Bounds checks on all array accesses
> \item  No  unions  that  include  a reference  type  (array,  @class@,
>    pointer, or @struct@ including such a type)
> \item No pointer arithmetic
> \item No escape of a pointer  or reference to a local variable outside
>    its scope
> \item Cross-module function calls must only go to other @safe@ modules
> \end{itemize*}
> So these are my thoughts so far. There is one problem though related to
> the last \item - there's no way for a module to specify "trusted",
> meaning: "Yeah, I do unsafe stuff inside, but safe modules can call me
> no problem". Many modules in std fit that mold.
> How can we address that? Again, I'm looking for a simple, robust,
> extensible design that doesn't lock our options.
> Thanks,
> Andrei

One comment that came up in discussing GC stuff in Bugzilla:  How do you prevent
the following in SafeD?

auto arrayOfRefs = new SomeClass[100];
GC.setAttr(arrayOfRefs.ptr, GC.BlkAttr.NO_SCAN);

foreach(ref elem; arrayOfRefs) {
    elem = new SomeClass();
}