opNext: Simplified ranges

[Joseph Rushton Wakeling]

On Saturday, 5 November 2022 at 06:01:54 UTC, Tomer at Weka wrote:
> ```
> bool opNext(out T elem) {...}
> ```
>
> `opNext` returns true if it "produced" an element, false if it 
> reached the end.

Out of curiosity: what do you think are the pros and cons of this 
versus, say, something like:

```
Option!(T) opNext() { ... }
```

Where `Option` is an implementation of the option type, and hence 
encapsulates the question of whether an element was produced or 
not?  (IIRC this has been another suggestion for a 
simplified/redesigned range concept.)

An `Option`-based design has the advantage of not requiring a 
persistent `front`, which may fit better with true input ranges 
(e.g. reading from a stream).  OTOH it may make things more 
clunky for the case where there is persistent underlying data 
that a `front` method could refer to.