c++ - Providing access to collection of abstract classes -

i designing interface (an abstract class) in c++ implements kind of tree structure: each instance has zero, one, or more children. children instances of interface.

i put quite thought interface not exclude particular implementations. example, methods should not return references forces implementation store value somewhere. exclude implementations recalculate value on each call; or wrappers transform returned value in way.

however, interface, unsure best way provide access children of instance. far, i've come 2 options:

class interface { public:      virtual ~interface() = default;      // idea 1: return collection of references.     virtual auto getchildren() const -> std::vector<std::reference_wrapper<interface>> = 0;      // idea 2: accept visitor.     virtual void visitchildren(const std::function<void(interface&)> &visitor) const = 0;  }; 

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my question: best* way provide access collection of abstract classes. other ideas , approaches appreciated (e.g. iterator-based approach, if @ possible).

*any or of following properties: idiomatic, flexible, scalable, maintainable, intuitive, semantically strongest, ...

placing discussion of design being java-like aside. if want close idiomatic c++, go iterators:

class interface {   class iterator_impl {     virtual ~iterator_impl() = default;     // fill rest   }; public:   class iterator {     std::unique_ptr<iterator_impl> _impl;     iterator(std::unique_ptr<iterator_impl> impl) : _impl(std::move(impl)) {}   public:     iterface& operator*() {       //forward _impl     }   };    virtual iterator begin() = 0;   virtual iterator end() = 0; }; 

after supplying complete iterator protocol, interface& can used in idiomatic c++ code:

void foo(interface& interface) {   for(auto& : interface) {     //do stuff   } }