Const ref and rvalues again...

[Malte Skarupke]

On Friday, 19 October 2012 at 00:03:49 UTC, Timon Gehr wrote:
>
> Const is different in D and in C++. Relating const and rvalues 
> is arbitrary and does not make a lot of sense.
>
> Regarding 'in ref'/'scope ref': What should 'scope' apply to in
>
> void foo(scope ref int* x);

Not sure what you mean with "relating." I'm not making any claims 
about there being a relationship between rvalues and constness.

This is about finding a way that you can define a function which 
safely accepts lvalues and rvalues without having to make a copy. 
If we specify the argument as "ref in", then we can safely pass 
for example the number 5 to it. And this would never break 
existing code, so that something like swap(5, 4) would never be 
possible code.

For the example that you gave you'd be unable to store the 
address of x. So doing

int** storage;
void foo(scope ref int * x)
{
     storage = &x;
}

would be illegal.

@jerro: the same thing: I'm not trying to fix the problem that 
you mention. I'm trying to define a function which can safely 
accept rvalues and lvalues without having to make a copy.