Opportunities for D

[Walter Bright via Digitalmars-d]

On 7/11/2014 4:44 AM, Nick Treleaven wrote:
> On 10/07/2014 19:03, Walter Bright wrote:
>> On 7/10/2014 9:00 AM, Nick Treleaven wrote:
>>> On 09/07/2014 20:55, Walter Bright wrote:
>>>>    Unique!(int*) u = new int;   // must work
>>>
>>> That works, it's spelled:
>>>
>>> Unique!int u = new int;
>>
>> I'm unconfortable with that design, as T can't be a class ref or a
>> dynamic array.
>
> It does currently work with class references, but not dynamic arrays:
>
>      Unique!Object u = new Object;
>
> It could be adjusted so that all non-value types are treated likewise:
>
>      Unique!(int[]) v = [1, 3, 2];
>
>>>>    int* p = new int;
>>>>    Unique!(int*) u = p;         // must fail
>>>
>>> The existing design actually allows that, but nulls p:
>>  > [...]
>>> If there are aliases of p before u is constructed, then u is not the
>>> sole owner
>>> of the reference (mentioned in the docs):
>>> http://dlang.org/phobos-prerelease/std_typecons.html#.Unique
>>
>> Exactly. It is not checkable and not good enough.
>
> In that case we'd need to deprecate Unique.this(ref RefT p) then.
>
>> Note that as of 2.066 the compiler tests for uniqueness of an expression
>> by seeing if it can be implicitly cast to immutable. It may be possible
>> to do that with Unique without needing compiler modifications.
>
> Current Unique has a non-ref constructor that only takes rvalues. Isn't that
> good enough to detect unique expressions?

No, see the examples I gave earlier.