Any way to do a binary tree traversal without `opApply` and allocations?

[solidstate1991]

On Thursday, 26 March 2026 at 22:48:22 UTC, Kapendev wrote:
>
> https://forum.dlang.org/thread/shqwthzzrrorowdqczzs@forum.dlang.org
>
> I think theres better ways to do it then this gist but 
> intrusive lists
>
> Im unsure what problems you have with the anti-work keywords, 
> but you have at least three options with what ive seen:
>
> smart handles: mixin+index, limits you to 1 array but elements 
> know where root is implicitly
>
> add indexes to your types: assume the root is index 0 or 1, 
> then you should be able to generate a range from the array
>
> add an index array to your datastructure.

It's a binary tree, where the "indexes" are keys, not exact 
locations, so that won't work.

I think I'll try again tomorrow, and also write a DIP to get 
around this issue, likely some change to the `opApply` function 
itself.

In the meanwhile, I might just add some Rust-style foreach with a 
template and a lambda.