ref is unsafe

[Nick Treleaven]

On 31/12/2012 14:44, Nick Treleaven wrote:
> On 30/12/2012 22:01, Jonathan M Davis wrote:
>> The closest that we could get to what you suggest would be to add a new
>> attribute similar to nothrow but which guarantees that the function
>> does not
>> return a ref to a parameter. So, you'd have to mark your functions
>> that way
>> (e.g. with @norefparamreturn). Maybe the compiler could infer it for
>> templated
>> ones, but this attribute would basically have to work like other inferred
>> attributes and be marked manually in all other cases. Certainly, you
>> can't
>> have the compiler figuring it out for you in general, because D's
>> compilation
>> model allows the function being called to be compiled separately from
>> (and
>> potentially after) the function calling it.
>
> As you suggested below that, I would have the attribute mean the
> opposite, @refparamreturn. Functions that need it but don't have it can
> be detected by recompiling them. The syntax could be 'in ref':
>
> in ref int quux(ref int i);

Actually overloading 'in ref' with a different meaning on return type 
from parameter (const scope) is probably a bad idea. Instead:

ref int quux(@escape ref int i);

[...]
> I suppose a parameter attribute might be useful to allow passing locals
> to other ref parameters which aren't returned, and as documentation.
>