any.h

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#ifndef STDEXT_ANY_H
#define STDEXT_ANY_H
 
#include <algorithm>
#include <cassert>
#include <typeinfo>
 
namespace stdext {
 
class any {
public:
    struct placeholder {
        virtual ~placeholder()  { }
        virtual const std::type_info& type() const = 0;
        virtual placeholder* clone() const = 0;
    };
 
    template<typename T>
    struct holder : public placeholder {
        holder(const T& value) : held(value) { }
        const std::type_info& type() const { return typeid(T); }
        placeholder* clone() const { return new holder(held); }
        T held;
    private:
        holder& operator=(const holder &);
    };
 
    placeholder* content;
 
    any() : content(nullptr) { }
    any(const any& other) : content(other.content ? other.content->clone() : nullptr) { }
    template<typename T> any(const T& value) : content(new holder<T>(value)) { }
    ~any() { delete content; }
 
    any& swap(any& rhs) { std::swap(content, rhs.content); return *this; }
 
    template<typename T> any& operator=(const T& rhs) { any(rhs).swap(*this); return *this; }
    any& operator=(any rhs) { rhs.swap(*this); return *this; }
 
    bool empty() const { return !content; }
    template<typename T> const T& cast() const;
    const std::type_info & type() const { return content ? content->type() : typeid(void); }
};
 
template<typename T>
const T& any_cast(const any& operand) {
    assert(operand.type() == typeid(T));
    return static_cast<any::holder<T>*>(operand.content)->held;
}
 
template<typename T> const T& any::cast() const { return any_cast<T>(*this); }
 
}
 
#endif