Actually I can see now that my last message contains few errors. On 22/03/2012 15:44, Bronek Kozicki wrote:
So do we want to change boost::sort( Rng& ) to boost::sort( Rng&& ) ? That would make boost::sort( std::vector() ) ok.
I fail to see what's wrong with this. Pointless - yes, but inducing runtime errors - no. Although of course I could have missed something.
Back to your function - perhaps taking unqualified template parameter is not the best idea, and if you want to take a range you might want to
... or perhaps not. Taking unqualified template parameter will allow you to write single function on anything with range-like interface, including boost::iterator_range itself. So, is there anything wrong with: template <typename Range> modifies_range(Range && rng); ?
C++ decided at some point to disallow binding rvalues to lvalue&. I think the reason is that rvalues are inaccessible for the caller, so modifying them is likely a bug.
on second reading I can see that you asked about exactly the opposite binding, taking the history back to last century :) Hope someone will find the explanation below helpful, but the context in which I have put it is obviously wrong - since it only applies to C++11 :)
no, the reason was different. The function which takes rvalue-reference does it in order to apply optimization (move semantics) which is often/easily implemented as "stealing" data from its actual parameter. If binding lvalues to rvalue-reference parameters was allowed, such "stealing" could happen implicitly, on an lvalue parameter, and would likely result in runtime errors. As things stand now, you have to be explicit about moving data away from lvalues, e.g. by using std::move()
B.