aliasing expressions and identifiers

[Marc Schütz via Digitalmars-d]

On Monday, 23 May 2016 at 15:18:51 UTC, Nick Treleaven wrote:
> On Monday, 23 May 2016 at 14:05:43 UTC, deed wrote:
>> Some thoughts about extending the with-statement were brought 
>> up here earlier:
>> http://forum.dlang.org/post/txpifmwpmmhsvcpbcijw@forum.dlang.org
>> I don't care much whether it would be with, alias or possibly 
>> something clever already existing, but a solution should be 
>> easy to use, easy to read and shouldn't introduce any possible 
>> overhead at runtime.
>
> From the linked thread:
>
>>        ref M()   { return matrix.rawArr; }
>>        ref Ex1() { return e1.someProperties.someModulusX; }
>
> If we had local refs, we could use this instead:
>
> ref m = matrix.rawArr;
>

Note that this wouldn't work with rvalues, which `with` supports.

> The difference is m is already computed, it is not recomputed 
> each time m is read, unlike M(). I think the reason D doesn't 
> support local refs is because it would make it harder to design 
> @safe, particularly with the planned @rc ref-counting. Because 
> M() above is only a return reference, it can't live longer than 
> the data it references. My ref m could persist longer than 
> matrix.rawArr using (naive) reference counting.

At some point during the `scope` discussion, Walter wanted to 
allow local `ref`s, so I guess he's not opposed to the idea. As 
far as I understand, the compiler already supports them 
internally, as they can result from lowering certain constructs, 
there's just no syntax for them. They wouldn't pose a problem for 
lifetime tracking, because they can never be assigned to, only 
initialized once.