merkle reverse

[Seb]

On Thursday, 5 April 2018 at 09:24:31 UTC, SimonN wrote:
> On Thursday, 5 April 2018 at 09:07:52 UTC, Seb wrote:
>> FYI: The problem isn't chunks, but that strings aren't 
>> bi-directional ranges (hello ugly auto-decoding!).
>> "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b".byCodeUnit
>
> Thanks! Very appropriate because it's all hex digits anyway.
>
> Instead of std.experimental.all, one can also import std.utf.
>
> Initially, I wondered whether autodecoding was the issue here, 
> but I dismissed it because the OP's example calls retro 
> immediately on a string, which is supposedly not autodecodable 
> as bi-directional. But I should examine retro's implementation 
> because I remember several Phobos functions having special 
> cases for strings (which is exactly the issue of auto-decoding).

Well sorry for my poor words.
Strings are bi-directional ranges, but they aren't random-access 
nor have a length which is typically required by other ranges to 
forward bidirectionality.

chunks requires hasSlicing + hasLength:

https://github.com/dlang/phobos/blob/193c61d985a9645014b2161b59ddb8692308e063/std/range/package.d#L7851

slide requires just hasSlicing:

https://github.com/dlang/phobos/blob/193c61d985a9645014b2161b59ddb8692308e063/std/range/package.d#L8650

Now why does "aa"[0.. 1] work, but hasSlicing return false?
Because it's explicitly excluded:

https://github.com/dlang/phobos/blob/193c61d985a9645014b2161b59ddb8692308e063/std/range/primitives.d#L1557

tl;dr: if you want to do anything useful with strings, byCodeUnit 
is usually your best friend.