Would like to see ref and out required for function calls

[Nick Treleaven]

On 13/09/2012 16:29, David Piepgrass wrote:
> On Thursday, 13 September 2012 at 15:01:28 UTC, Andrei Alexandrescu wrote:
>> On 9/13/12 10:53 AM, David Piepgrass wrote:
>>>> Walter and I have discussed this for quite a while. We have recently
>>>> decided to disallow, at least in SafeD, escaping the address of a ref
>>>> parameter. In the beginning we'll be overly conservative by
>>>> disallowing taking the address of a ref altogether. I'll write a DIP
>>>> on that soon.
>>>
>>> Err, wouldn't that break a lot of stuff, a lot of which is actually safe
>>> code?
>>>
>>> void a(ref int x) { b(&x); }
>>> void b(int* x) { if(x != null) (*x)++; }
>>
>> Yes. Disallowing taking the address of a local is conservative and
>> would disallow a number of valid programs.

What about:

void b(scope int* x) { if(x != null) (*x)++; }

Then 'a' could compile safely.

>> Arguably, such programs are in poor style anyway. A good program takes
>> pointers only if it needs to keep them around; if all that's needed is
>> to use the parameter transitorily or pass it down, ref is best.
>
> Another common reason to use a pointer (instead of ref) is if it's
> optional (nullable). If the parameter is ref then the caller must go to
> the trouble of creating a variable.

Maybe std.typecons.Nullable or something like it helps there.