Re: [boost] Re: looping construct

From: John Torjo (john.lists_at_[hidden])
Date: 2004-04-23 02:24:05

Eric Niebler wrote:

> Anatoli Tubman wrote:
>
>> John Torjo wrote:
>>
>>> However, had I used
>>> crange<int> r(d); // how do I know what iterators to keep inside?
>>> crange<int> r(v); // how do I know what iterators to keep inside?
>>
>>
>> You keep a pointer to crange_impl_base<int> which points to a
>> heap-allocated instance of crange_impl<int, d_array>
>
>
> Nope. :-)
>
>
>> Another option is to write
>>
>>   for (crange<int>& r = mkrange(d); r; ++r) { ... }
>>
>> where mkrange returns crange_impl<int, d_array> which is derived from
>> crange<int>.
>>
>> This doesn't need heap allocation, but still needs virtual operator++
>> and virtual operator*.
>
>
>
> Not that either. :-) With the FOREACH macro, you don't have to specify 
> the container type, there is no heap allocation and no virtual 
> function calls. Everything is fully-inline-able. And it doesn't need 
> typeof.
>

Your technique is indeed very cool and useful, when you want to only go 
forward ;)

The problem is if you need "custom incrementing". Like, sometimes you 
might want to go back, or twice forward and such. Or, when you need two 
consecutive values, like *r and *(r-1)

for ( crange<container> r(cont); r; ++r) {
    if ( *r == 10) {
       *(--r) = 0; ++r;
    }
}

Best,
John