Hello, I'm writing an small library to represent types. Right now I'm focusing on representing type composition. For that I'm using the composite pattern as proposed by Gamma et al., so I have an abstract base class for my composites that has the virtual functions to addComposite members, but not their implementation. The header of my class looks like this: namespace dintype { class Type{ public: virtual ~Type()=0; typedef std::string Name_t; virtual void addComposition(const Name_t& name,Type* tp)=0; virtual void delComposition(const Name_t& name)=0; Type* clone() const; protected: typedef ptr_map<Name_t,Type> children_t; typedef children_t::iterator children_iterator; typedef children_t::const_iterator children_const_iterator; typedef children_t::size_type children_size_type; Type(); private: virtual Type* do_clone() const=0; }; inline Type* new_clone(const Type& c) { return c.clone(); } } The one for my composite class is: class CompositeType : public Type { private: children_t m_children; CompositeType(const CompositeType& r); virtual Type* do_clone(); protected: void clearAllCompositeChildren(); public: CompositeType(); virtual ~CompositeType(); virtual void addComposition(const Name_t& name,Type* tp); virtual void delComposition(const Name_t& name); }; Here is the implementation of the composite class: CompositeType::CompositeType(const CompositeType& r) : m_children(r.m_children.clone()) { } CompositeType::CompositeType() { } CompositeType::~CompositeType() { } void CompositeType::clearAllCompositeChildren() { m_children.erase(m_children.begin(),m_children.end()); } void CompositeType::addComposition(const Name_t& name,Type* tp) { m_children[name]=tp; // <========= THIS LINE IS THE PROBLEM } void CompositeType::delComposition(const Name_t& name) { m_children.erase(name); } I can't get the program to compile because gcc keeps complaining m_children[name] don't has operator= and that type is an abstract class and can't be initialized. I read all the boost::prt_container documentation and I couldn't find what I'm doing wrong. I also tried m_children.insert(name,tp); to no avail. I'll greatly appreciate any help. Thanks, Gustavo