DIP23 draft: Fixing properties redux

[Andrei Alexandrescu]

On 2/5/13 2:05 PM, Steven Schveighoffer wrote:
> On Tue, 05 Feb 2013 13:33:35 -0500, Andrei Alexandrescu
> <SeeWebsiteForEmail at erdani.org> wrote:
>
>> Walter and I reviewed the discussion and had a long talk. We are very
>> seriously considering banning the use of & against a ref result from a
>> function (and actually ref parameters and even struct members in @safe
>> code). One would still be able to take the address of a field in a
>> class because that's assumed to live on the GC heap.
>
> What about structs that live on the heap? e.g. a struct element of an
> array, or a struct member of a class instance.

In that case we'll disallow it conservatively.

> I think the point about @safe code is moot, aren't pointers disallowed
> in safe code anyway?

Yah, time to start enforcing it more seriously. But we want to ban some 
uses of & in all code.

>> To get the address of an object in @system code without resorting to
>> operator& at all, we're considering adding a stdlib function
>> implemented like this (there are several other ways, this is just for
>> illustration):
>>
>> @system T* addressOf(T)(ref T obj)
>> {
>> static T* id(T* p) { return p; }
>> auto idr = cast(T* function(ref T)) id;
>> return idr(obj);
>> }
>
>
> I think a cast would be sufficient:
>
> cast(int *)(&refparam); // understood that a cast is required
>
> To jump through this machinery to turn a reference into a, um...
> reference, seems like a huge waste of code space and resources.

The whole point was to avoid using operator &.


Andrei