Safety, undefined behavior, @safe, @trusted

[Walter Bright]

Jason House wrote:
> I posted in the other thread how casting to immutable/shared can be
> just as bad. A leaked reference prior to casting to immutable/shared
> is in effect the same as casting away shared. No matter how you mix
> thread local and shared, or mutable and immutable, you still have the
> same undefined behavior

Not undefined, it's just that the compiler can't prove it's defined 
behavior. Hence, such code would go into a trusted function.