called copy constructor in foreach with ref on Range

[Sebastiaan Koppe]

On Tuesday, 23 June 2020 at 07:30:29 UTC, Stanislav Blinov wrote:
> On Tuesday, 23 June 2020 at 05:24:37 UTC, H. S. Teoh wrote:
>> I'm also wondering what's the motivation behind supporting 
>> non-copyable ranges, and whether it's worth the effort and 
>> inevitable complications to support it if it's a rare use-case.
>>  Do you have any compelling use-case in mind, that might make 
>> this worthwhile?
>
> This compelling use case is staring at us from comments in this 
> very thread.

I am a bit on the fence about having input ranges be 
non-copyable. Initially I liked the idea very much; I am a big 
fan of 'unique' semantics.

But just because most people don't expect hot/destructive reads, 
doesn't mean we should impose such a hard restriction on input 
ranges. There are use cases for popping from an input range from 
different places. An obvious one would be parsing data from the 
network, where you pass the input range into helper functions 
that parse sub-sections of the data.

They can be made to work for sure, but it doesn't make it cleaner.

On the other hand, most of the time, non-copyable is exactly what 
you need...