Forward ranges in Phobos v2

[Alexandru Ermicioi]

On Tuesday, 2 November 2021 at 20:17:06 UTC, Andrei Alexandrescu 
wrote:
> On 2021-11-02 15:32, Adam D Ruppe wrote:
>> On Tuesday, 2 November 2021 at 18:09:55 UTC, H. S. Teoh wrote:
>>> Why is this necessary?  I thought we're getting rid of 
>>> std.range.interfaces.
>> 
>> It is actually really, really, useful. If phobos didn't offer 
>> it, someone would reinvent it anyway.
>> 
>> (In fact, there's a lot of cases where using them is more 
>> efficient than generating more and more code...)
>
> Yah, polymorphism has its place. The only problem is passing 
> around reference ranges. They should have a thin struct wrapper 
> that carries the proper copy semantics.

So, if forward range interface (from std.range.interfaces) is to 
be kept in phobos, it should provide a .save method, that can be 
used instead of copy constructor.

Then, it is possible to have only one wrapper struct for 
transforming it into value type (i.e. behave same as struct 
forward range), that would use .save when wrapper's copy 
constructor is invoked. It would allow to use this wrapper as 
part of method parameter type, in order to enforce people using 
it, and not randomly forgetting to wrap it.