c++ - Writing traversal methods for classes (TreeNode) that are designed to be inside (arbitrary) containers -

i have class (when simplified) looks this:

class treenode {     ptrdiff_t sibling_offset, first_child_offset; public:     long whatever;      // ... }; 

the tree nodes must contain offsets instead of pointers, because needs possible them embedded in containers (like std::vector) may reallocate storage when necessary, without having spend time re-linking nodes.

now, if have suitably defined class treeiterator<iter> (perhaps defined friend of treenode) job iterate on treenode's children, any stl-style client of class should able use iterate on children of node in standard, stl fashion:

typedef std::vector<treenode> tree; tree tree = ...;  treeiterator<tree::iterator> const root = tree.begin(); (treeiterator<tree::iterator> = root->begin(); != root->end(); ++i) {     foo(i->whatever);     process_further(i); } 

the trouble is, root->begin() impossible because treenode doesn't know container it's in.
(and shouldn't! thing cares container has suitable iterators.)

and yet, i (the author of treenode) 1 possibly how iterate on children.

how resolve issue, without restricting type of container treenode may stored in?

obviously easy if force user use std::vector, should free use arbitrary stl-compliant container.

you define functions begin() , end() in treenode. , use them in code.

    class treenode {         ...         std::vector<t>::iterator begin() {return vec.begin();}         std::vector<t>::iterator end()   {return vec.end();}         ...     private:         std::vector<t> vec;     }