mariadb-columnstore-engine/utils/common/any.hpp

#pragma once
/*
 * (C) Copyright Christopher Diggins 2005-2011
 * (C) Copyright Pablo Aguilar 2005
 * (C) Copyright Kevlin Henney 2001
 *
 * Distributed under the Boost Software License, Version 1.0. (See
 * accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt
 */

#include <stdexcept>

namespace static_any
{
namespace anyimpl
{

	struct bad_any_cast 
	{
	};

	struct empty_any 
	{
	};

	struct base_any_policy 
	{
		virtual void static_delete(void** x) = 0;
		virtual void copy_from_value(void const* src, void** dest) = 0;
		virtual void clone(void* const* src, void** dest) = 0;
		virtual void move(void* const* src, void** dest) = 0;
		virtual void* get_value(void** src) = 0;
		virtual size_t get_size() = 0;
	};

	template<typename T>
	struct typed_base_any_policy : base_any_policy
	{
		virtual size_t get_size() { return sizeof(T); } 
	};

	template<typename T>
	struct small_any_policy : typed_base_any_policy<T>
	{
		virtual void static_delete(void** x) { }
		virtual void copy_from_value(void const* src, void** dest)
			{ new(dest) T(*reinterpret_cast<T const*>(src)); }
		virtual void clone(void* const* src, void** dest) { *dest = *src; }
		virtual void move(void* const* src, void** dest) { *dest = *src; }
		virtual void* get_value(void** src) { return reinterpret_cast<void*>(src); }
	};

	template<typename T>
	struct big_any_policy : typed_base_any_policy<T>
	{
		virtual void static_delete(void** x) { if (*x) 
			delete(*reinterpret_cast<T**>(x)); *x = NULL; }
		virtual void copy_from_value(void const* src, void** dest) { 
		   *dest = new T(*reinterpret_cast<T const*>(src)); }
		virtual void clone(void* const* src, void** dest) { 
		   *dest = new T(**reinterpret_cast<T* const*>(src)); }
		virtual void move(void* const* src, void** dest) { 
		  (*reinterpret_cast<T**>(dest))->~T(); 
		  **reinterpret_cast<T**>(dest) = **reinterpret_cast<T* const*>(src); }
		virtual void* get_value(void** src) { return *src; }
	};

	template<typename T>
	struct choose_policy 
	{
		typedef big_any_policy<T> type;
	};

	template<typename T> 
	struct choose_policy<T*> 
	{ 
		typedef small_any_policy<T*> type; 
	};

	struct any;

	/// Choosing the policy for an any type is illegal, but should never happen.
	/// This is designed to throw a compiler error.
	template<>
	struct choose_policy<any>
	{
		typedef void type;
	};

	/// Specializations for small types.
	#define SMALL_POLICY(TYPE) template<> struct \
	   choose_policy<TYPE> { typedef small_any_policy<TYPE> type; };

	SMALL_POLICY(char);
	SMALL_POLICY(signed char);
	SMALL_POLICY(unsigned char);
	SMALL_POLICY(signed short);
	SMALL_POLICY(unsigned short);
	SMALL_POLICY(signed int);
	SMALL_POLICY(unsigned int);
	SMALL_POLICY(signed long);
	SMALL_POLICY(unsigned long);
	SMALL_POLICY(signed long long);
	SMALL_POLICY(unsigned long long);
	SMALL_POLICY(float);
	SMALL_POLICY(double);
	SMALL_POLICY(bool);

	#undef SMALL_POLICY

	/// This function will return a different policy for each type. 
	template<typename T>
	base_any_policy* get_policy()
	{
		static typename choose_policy<T>::type policy;
		return &policy;
	};
}

class any
{
private:
    // fields
    anyimpl::base_any_policy* policy;
    void* object;

public:
    /// Initializing constructor.
    template <typename T>
    any(const T& x) 
        : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) 
    {
        assign(x);
    }       

    /// Empty constructor. 
    any() 
        : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) 
    { }

    /// Special initializing constructor for string literals. 
    any(const char* x) 
        : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) 
    { 
        assign(x);
    }

    /// Copy constructor. 
    any(const any& x) 
        : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL)         
    {            
        assign(x);
    }

    /// Destructor. 
    ~any() {
        policy->static_delete(&object);
    }

    /// Assignment function from another any. 
    any& assign(const any& x) {
        reset();
        policy = x.policy;
        policy->clone(&x.object, &object);
        return *this;
    }

    /// Assignment function. 
    template <typename T>
    any& assign(const T& x) {
        reset();
        policy = anyimpl::get_policy<T>();
        policy->copy_from_value(&x, &object);
        return *this;
    }

    /// Assignment operator.
    template<typename T>
    any& operator=(const T& x) {
        return assign(x);
    }

    /// Assignment operator, specialed for literal strings. 
    /// They have types like const char [6] which don't work as expected. 
    any& operator=(const char* x) {
        return assign(x);
    }

    /// Utility functions
    any& swap(any& x) {
        std::swap(policy, x.policy);
        std::swap(object, x.object);
        return *this;
    }

    /// Cast operator. You can only cast to the original type.
    template<typename T>
    T& cast() {
        if (policy != anyimpl::get_policy<T>()) 
            throw anyimpl::bad_any_cast();
        T* r = reinterpret_cast<T*>(policy->get_value(&object)); 
        return *r;
    }

    /// Returns true if the any contains no value. 
    bool empty() const {
        return policy == anyimpl::get_policy<anyimpl::empty_any>();
    }

    /// Frees any allocated memory, and sets the value to NULL.
    void reset() {
        policy->static_delete(&object);
        policy = anyimpl::get_policy<anyimpl::empty_any>();
    }

    /// Returns true if the two types are the same. 
    bool compatible(const any& x) const {
        return policy == x.policy;
    }
};
}