The liabilities of binding rvalues to ref

[Peter Alexander]

On Thursday, 9 May 2013 at 04:00:55 UTC, Manu wrote:
> Perhaps you're arguing that the problem is that the user 
> _isn't_ getting
> compiler complaints when the code is changed? The call that 
> modifies it
> will still work fine, but it will obviously apply the changes 
> to a temp
> that is then lost? Surely this is to be expected?

The call will not still work fine in C++.

Here's the code again:

class Collection(T) {
   ref T opIndex(size_t i) { ... }
   ...
}

void fix(ref double x) { if (isnan(x)) x = 0; }

void fixAll(Collection!double c) {
   foreach (i; 0 .. c.length) {
     fix(c[i]);
   }
}


In (analogous) C++, if Collection's opIndex changes to return by 
value then the call to fix is a compile time error (the rvalues 
don't bind to unqualified ref). I believe Andrei is arguing that 
D must _at least_ do this to make progress, i.e. not be "worse" 
(than C++).