[boost] Re: Re: FOREACH / C++ "for" proposal

From: Thorsten Ottosen (nesotto_at_[hidden])
Date: 2005-05-13 07:54:22

"Peter Dimov" <pdimov_at_[hidden]> wrote in message 
news:006f01c557b3$934ff320$6f01a8c0_at_pdimov...
| Thorsten Ottosen wrote:
|
| >> Note that there is no need for an rvalue reference here unless you
| >> really want to allow people to change a non-const rvalue in a for
| >> loop:
| >>
| >> for( char& i: MyContainer() )
| >> {
| >>    ++i; // questionable
| >> }
| >
| > it seems to be very useful if you're chaining algorithms that all
| > acts on rvalues.
|
| Yes, I understand your motivation for using an rvalue reference now. But I
| still think that you don't need it.
|
| template<class C> ... my_view( C && c )
| {
|    begin(c); // c is lvalue here!
|    end(c); // ditto
| }

true.

and that part of the proposal is not really specified yet.

| > still, we need two version of each function, the && version and the
| > const & version.
|
| No :-)
|
| The && / const& overloading is only ever used with move. It directs
| non-const rvalues to && (safe to move) and everything else to const& (not
| safe to move). In your case this would mean that you'll get the const
| overload for non-const lvalues. I doubt that you wanted that to happen.

doh again :-)

so begin()/end() would need to be overloaded for
& and const&, just like today.

| But we got carried away.
|
| My main point was that your proposed core extension depends on too many
| things in the C++ world to conform to your vision of the future. This can be
| acceptable and even desirable in a library proposal, but would be counted
| against a core language proposal. A language change should be as
| self-contained and as independent of other proposals - language or library -
| if you want to increase the chances of its acceptance. In my opinion.

you should have seen the version I presented in Redmond then :-)

anyway, I should state that no dependency on move-semantics is needed.

-Thorsten