The liabilities of binding rvalues to ref

[deadalnix]

On Sunday, 5 May 2013 at 16:14:01 UTC, Dicebot wrote:
> Few additional points:
>
> On Sunday, 5 May 2013 at 16:07:12 UTC, deadalnix wrote:
>> I wish to add to the discussion that you want to pass by ref 
>> for 2 reasons (and the intent is very different) :
>> - You intend to modify the value in some meaningful way for 
>> the caller. In which case, binding to rvalue don't make any 
>> sense.
>
> You may want to modify rvalue temporary for implementing some 
> sort of move semantics like in C++11.
>

No, you won't be able to reach any of this anyway. Move semantic 
is already cleanly implemented in D, so the C++ mess is 
irrelevant here.

>> - You want to avoid creating copies, when this isn't 
>> necessary. In this case, this is a performance reason, and 
>> binding to rvalue make sense.
>
> Not necessarily performance reason on its own, copy 
> construction of given object may have an undesired side 
> effects. Or it may be even some singleton'ish object.

Having a singleton as a value type, and not marking the postblit 
as @disable is asking for trouble in general, nothing specific to 
the discussion here.