ref is unsafe

[Jonathan M Davis]

On Monday, December 31, 2012 22:25:52 Mehrdad wrote:
> I don't understand why there is a discussion on trying to
> special-case ref parameters. There's nothing special about ref
> parameters... what's special is ref _returns_.
> 
> Therefore all we need to do is disallow ref returns in @safe code.

The problem is ranges. auto ref returns are _very_ common with the front and 
back of ranges (especially wrapper ranges). If returning by ref or auto ref 
automatically renders code @system, then we just made a _large_ portion of 
Phobos @system when most of it is actually perfectly safe.

We _might_ be able to say that a function is @system if it both takes an 
argument by ref and returns by ref, but even that is likely to be a problem 
unless we can statically prove _in most cases_ that there's no way that the 
ref being returned could be to any portion of any of the arguments passed by 
ref.

- Jonathan M Davis