C++ Any类型实现

男娘i 2022-06-12 04:19 216阅读 0赞

**C++ Any类型实现**

在java或c\#中，Object类型对象可以指向任意类型的变量，因为所有的类默认都从Object类继承。但是在c++中，没有类似Object类这样的类型，而很多时候，为了设计出通用的程序，往往需要类似于Object类型作为参数或者返回值。

class any { public: // structors any() : content(0) { } template<typename ValueType> any(const ValueType & value) : content(new holder<ValueType>(value)) { } any(const any & other) : content(other.content ? other.content->clone() : 0) { } ~any() { delete content; } public: // modifiers any & swap(any & rhs) { std::swap(content, rhs.content); return *this; } template<typename ValueType> any & operator=(const ValueType & rhs) { any(rhs).swap(*this); return *this; } any & operator=(any rhs) { rhs.swap(*this); return *this; } public: // queries bool empty() const { return !content; } const std::type_info & type() const { return content ? content->type() : typeid(void); } public: // types (public so any_cast can be non-friend) class placeholder { public: // structors virtual ~placeholder() { } public: // queries virtual const std::type_info & type() const = 0; virtual placeholder * clone() const = 0; }; template<typename ValueType> class holder : public placeholder { public: // structors holder(const ValueType & value) : held(value) { } public: // queries virtual const std::type_info & type() const { return typeid(ValueType); } virtual placeholder * clone() const { return new holder(held); } public: // representation ValueType held; private: // intentionally left unimplemented holder & operator=(const holder &); }; public: // representation (public so any_cast can be non-friend) placeholder * content; }; template<typename ValueType> ValueType any_cast(const any& operand) { assert(operand.type() == typeid(ValueType)); return static_cast<any::holder<ValueType> *>(operand.content)->held; }

参考链接：http://www.cnblogs.com/feixue/p/boost-any.html