foreach DFS/BFS for tree data-structure?

[Steven Schveighoffer]

On 6/14/18 8:35 AM, Robert M. Münch wrote:
> On 2018-06-14 11:46:04 +0000, Dennis said:
> 
>> On Thursday, 14 June 2018 at 11:31:50 UTC, Robert M. Münch wrote:
>>> Is this possible? I read about Inputranges, took a look at the RBTree 
>>> code etc. but don't relly know/understand where to start.
>>
>> You can also use opApply to iterate over a tree using foreach, see:
>> https://tour.dlang.org/tour/en/gems/opdispatch-opapply
> 
> Ah... that looks very good. Need to dig a bit deeper on how to use it. 
> Thanks.
> 

Just to clarify, RBTree can easily do DFS without a real stack because 
there are a finite number of children (2) for each node, and it's an 
O(1) operation to figure out which child the current node is in relation 
to the parent (am I a left child or right child?).

Now, with your C version, if your children are stored in the array 
itself, figuring out the "next" child is a matter of doing &this + 1. 
But if you are storing pointers instead, then figuring out the next 
child would be an O(n) operation.

Using the stack to track where you are (via opApply) is a valid way as 
well. You could also unroll that into a malloc'd stack, but the code is 
not as pretty of course.

-Steve