Call site 'ref'

[Peter Alexander]

On 15/01/12 10:36 PM, Timon Gehr wrote:
> On 01/15/2012 11:41 PM, Peter Alexander wrote:
>> On 15/01/12 10:10 PM, Timon Gehr wrote:
>>> Another thing that would have to be discussed: what happens to const ref
>>> parameters? It is very reasonable that someone will decide to change
>>> calling conventions from by value to by const ref or the other way round
>>> after profiling. It is very convenient that such a change is
>>> syntactically transparent to the caller and this should stay.
>>
>> Actually, that would be very dangerous. const ref does not have the
>> privilege of being able to bind to rvalues in D like it does in C++.
>>
>> void foo(const ref int x) {...}
>>
>> foo(1); // this is legal in C++, but illegal in D
>>
>
> Who on earth wants to change an int parameter from by value to by const
> ref? struct literals can bind to const ref parameters so there is
> absolutely no issue.

Are you sure about struct literals binding to const ref? I can't find 
anything in the language spec or TDPL that supports that claim.

In fact, TDPL says:

"If a function expects a ref, it accepts only "real" data, not 
temporaries; anything that's not an lvalue is rejected during compilation"

Unfortunately it doesn't say anything explicitly about struct literals 
or const ref, but that would lead me to believe that they fall under the 
same rule.

DMD allows struct literals to bind to const ref, but then again it also 
allows them to bind to ref, so I'm not sure how reliable that is.

This should probably be clarified. It's kind of important.