The liabilities of binding rvalues to ref

[Peter Alexander]

On Thursday, 9 May 2013 at 18:23:12 UTC, Steven Schveighoffer 
wrote:
> On Thu, 09 May 2013 13:45:16 -0400, Peter Alexander
>> Allowing plain-old ref to bind to rvalues would be a massive 
>> mistake in my opinion. See case (2) in the original post.
>
> The case for it is operator overloads.  Note that all operator 
> overloads are defined WITHIN types, and all operator overloads 
> take 'this' by reference.  Without the hack currently in the 
> compiler that 'this' is allowed to bind by ref to rvalues, D 
> would be near useless.

C++ has this "hack" as well. Is it really a hack, or just part of 
the language design?


> Consider that today, this doesn't work for custom structs, 
> unless you allocate the result on the heap.
>
> ((a + b) + (c + d))

I don't follow. You say "today", but this works for me in latest 
dmd. Do you mean hypothetically without the "hack", or am I 
misunderstanding?


> The original case 2 looks bad, but not very common.  With 
> by-ref turning into by-value, you are in effect changing the 
> API and functionality.  It would just mean that you wouldn't 
> make that change, or change the type name at the same time (so 
> it wouldn't just compile on existing code).

I'm not sure about how common it is, but I really don't like the 
idea of calls like swap(1, 2) being legal. Seems like a step 
backward from C++.