DIP74 updated with new protocol for function calls

[Matthias Bentrup via Digitalmars-d]

On Sunday, 1 March 2015 at 07:04:09 UTC, Zach the Mystic wrote:
> On Saturday, 28 February 2015 at 21:12:54 UTC, Andrei 
> Alexandrescu wrote:
>> Defines a significantly better function call protocol:
>>
>> http://wiki.dlang.org/DIP74
>>
>> Andrei
>
> This is obviously much better, Andrei.
>
> I think an alternative solution (I know -- another idea -- 
> against my own first idea!) is to keep track of this from the 
> caller's side. The compiler, in this case, when copying a 
> ref-counted type (or derivative) into a parameter, would 
> actually check to see if it's splitting the variable in two. 
> Look at this:
>
> class RcType {...}
>
> void fun(RcType1 c, RcType1 d);
>
> auto x = new RcType;
>
> fun(x, x);
>
> If the compiler were smart, it would realize that by splitting 
> parameters this way, it's actually adding an additional 
> reference to x. The function should get one x for free, and 
> then force an opAdd/opRelease, for every additional x (or x 
> derivative) it detects in the same call.
>
> This might be even better than the improved current proposal. 
> The real key is realizing that duplicating an lvalue into the 
> same function call is subtly adding a new reference to it.
>
> Eh??

Note that you can get the same issue without duplicate 
parameters, if you pass an alias to a global variable.


static A a;

void fun(A x) {
   a = null; // Releases x
   x.func();
}

void main() {
   a = new A();
   fun(a);
}