bool empty() const for ranges

[Stanislav Blinov]

On Friday, 26 November 2021 at 10:44:10 UTC, Salih Dincer wrote:

> * Is the const essential for ranges?
> * Is it possible to rewind the pointer (```Node * head;```) 
> when my head is empty by the const?

`empty` is not required to be `const`, but it is required to 
yield the same result if called multiple times without mutating 
the range (see 
https://dlang.org/phobos/std_range_primitives.html#.isInputRange). In other words, you really ought not to mutate the range in implementation of `empty`, or at least not to the extent you seem to want to.