Plan for InputRange?

[Dukc]

On Wednesday, 29 September 2021 at 06:10:30 UTC, bauss wrote:
> Why should it throw an exception when you can detect it at 
> compiletime?
>
> ```
> override E moveFront()
> {
>     static if (__traits(compiles, r.moveFront))
>         return r.moveFront;
>     else
>         static assert(0, "Cannot move the front of a `" ~ 
> typeof(r).stringof ~ "`");
> }
> ```

`inputRangeObject` already does something like that, but there 
lies the problem. It means that you cannot wrap a range with 
immobile elements in any of the `std.range.primitives` at all, 
even if you never move them.

Perhaps it could do a regular `assert(false)` though. I'm not 
sure it should throw an exception, since calling `moveFront` 
where one is not implemented is a bug, not an environmental 
error. On the other hand catchable exceptions are the simplest 
way to let the user to introspect whether the elements are mobile.