The liabilities of binding rvalues to ref

[deadalnix]

On Friday, 10 May 2013 at 04:44:29 UTC, Jonathan M Davis wrote:
>> 2. We could say UFCS has an implicit ref-at-callsite if 
>> needed, and will
>> not compile for rvalues.  If you think about it, 'this' is 
>> implicitly ref,
>> and UFCS is calling like the first argument is the 'this' 
>> reference.
>
> That would make using UFCS with ranges generally illegal, as 
> most range-based
> funtions do not have ref parameters, and you generally don't 
> want them to be
> passed by ref.
>

Why ? Range behavior is undefined when passed by value.

> On the other hand, if ref at the callsite is optional, then the 
> lack of ref at
> the call site means absolutely nothing. You're still going to 
> have to look at
> every single function signature to determine if it takes a ref 
> argument or
> not, meaning that the lack of ref at the call site buys you 
> nothing at best
> and harms you at worst, because it gives you a false sense of 
> security that
> the argument is not being passed by ref. Programmers would have 
> to be 100%
> consistent in using ref at the callsite to avoid that, and 
> that's obviously
> not going to happen.
>

It make sense when you pass by ref to modify things. In this case 
passing an rvalue don't make any sense. If you di it for 
performance, then this is yet another instance of the compiler 
rewriting things to improve performances.