"the last change" for ranges

Andrei Alexandrescu SeeWebsiteForEmail at erdani.org
Wed May 20 11:44:54 PDT 2009

Jason House wrote:
> Andrei Alexandrescu Wrote:
>> Jason House wrote:
>>> I feel like there are too many differences between input and forward
>>> ranges for such a minor difference. Many range functions are written
>>> assuming no side effects on the caller. This can restrict the use of
>>> helper functions. It may be best to make their usage different...
>> So how do you think we should go about it? Also don't forget that any 
>> ranges should be seamlessly and efficiently treated as input ranges.
>> Andrei
> You won't like my answer!
> Like you've already said, the semantics of forward ranges and input ranges are different. I would argue that forward ranges have value semantics but input ranges do not. Any function that implicitly assumes value semantics is wrong. Sadly, overlapping API's makes that all too easy for someone to write bad code that passes simplistic tests with forward ranges and then fail with input ranges.
> My initial thoughts is that input ranges should have two changes:
> 1. A different API from forward ranges
> 2. Be a reference type (AKA class instead of struct)
> In short, I disagree with your basic premise of treating the two ranges similarly.

I don't want to treat them similarly, but we should be able to treat 
forward ranges as input ranges. Otherwise, all algorithms that work for 
input ranges would have to be written twice.


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