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

From: Peter Dimov (pdimov_at_[hidden])
Date: 2005-05-13 07:01:59

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
}

> 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.

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.