这儿的冒号是啥意思? 还有这个模版...
enum NodeType { BranchNode, AggregateNode, LeafNode }; class Node { public: NodeType type() const; protected: Node( NodeType type ); ~Node() {}; private: NodeType type_ : 2;//为什么用冒号? 是什么意思? };template< typename T, int AS = 1 >class Octree{ ...}