foreach, an analogy

[Walter Bright]

Sean Kelly wrote:
> Walter Bright wrote:
>>
>> How do you make for work with the following data structure:
>>
>>     struct Tree
>>     {    Tree* left;
>>         Tree* right;
>>         int data;
>>     }
>> ?
> The iterator would have to contain a stack of pointers to previously 
> visited nodes.

Yes, it's messy and complicated. A stack of pointers also means storage 
allocation issues.

> C++ tree containers don't have this problem because the 
> performance requirements require a balanced tree,

The iterator requirement is what's really driving the design of C++ 
containers. D's AAs deliver better performance than STL's trees.

> and nodes for such a 
> structure contain a pointer to the parent node as well.

I know. They're also *far* more complex. Take a look at the STL source 
for them. I wanted containers for D to be much easier to program.