meta/runtime/any.h

/**
 * Port of boost::any for C++11 compilers.
 * See http://www.boost.org/libs/any for Documentation.
 *
 * See also:
 *   + http://en.cppreference.com/w/cpp/any
 *   + http://en.cppreference.com/w/cpp/experimental/any
 *   + http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4562.html#any
 *   + https://cplusplus.github.io/LWG/lwg-active.html#2509
 *
 * Copyright Kevlin Henney, 2000, 2001, 2002. All rights reserved.
 * Copyright Claudio Fantacci, 2018. All rights reserved.
 *
 * what:  variant type boost::any
 * who:   contributed by Kevlin Henney,
 *        with features contributed and bugs found by Antony Polukhin, Ed Brey, Mark Rodgers, Peter Dimov and James Curran,
 *        with C++11 compiler port by Claudio Fantacci
 * when:  July 2001, April 2013 - May 2013, September 2018
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE.md or copy at http://www.boost.org/LICENSE_1_0.txt)
 */

#pragma once
#ifndef META_ANY_H
#define META_ANY_H

#include <algorithm>
#include <memory>
#include <stdexcept>
#include <type_traits>
#include <typeinfo>

namespace meta {
namespace reflection {

/**
 * The class any describes a type-safe container for single values of any type.
 * An object of class any stores an instance of any type that satisfies the
 * constructor requirements or is empty, and this is referred to as the state
 * of the class any object. The stored instance is called the contained object.
 * Two states are equivalent if they are either both empty or if both are not
 * empty and if the contained objects are equivalent.
 * The non-member any_cast functions provide type-safe access to the contained object.
 */
class any final {
public:
    /**
     * Constructs an empty object.
     */
    any() noexcept : content(0) {}

    /**
     * Copies content of other into a new instance, so that any content is equivalent
     * in both type and value to those of other prior to the constructor call,
     * or empty if other is empty.
     */
    any(const any &other) : content(other.content ? other.content->clone() : 0) {}

    /**
     * Moves content of other into a new instance, so that any content is equivalent
     * in both type and value to those of other prior to the constructor call,
     * or empty if other is empty.
     */
    any(any &&other) noexcept : content(other.content) { other.content = 0; }

    /**
     * Constructs an object with initial content an object of type std::decay_t<ValueType>,
     * direct-initialized from std::forward<ValueType>(value). If
     * std::is_copy_constructible<std::decay_t<ValueType>>::value is false, the program is ill-formed.
     */
    template<typename ValueType>
    any(const ValueType &value)
        : content(
            new holder<typename std::remove_cv<typename std::decay<const ValueType>::type>::type>(
                value))
    {}

    /**
     * Constructs an object with initial content an object of type std::decay_t<ValueType>,
     * direct-initialized from std::forward<ValueType>(value). If
     * std::is_copy_constructible<std::decay_t<ValueType>>::value is false, the program is ill-formed.
     */
    template<typename ValueType>
    any(ValueType &&value,
        typename std::enable_if<!std::is_same<any &, ValueType>::value>::type * = 0,
        typename std::enable_if<!std::is_const<ValueType>::value>::type * = 0)
        : content(
            new holder<typename std::decay<ValueType>::type>(static_cast<ValueType &&>(value)))
    {}

    /**
     * Destruct the object.
     */
    ~any() noexcept { delete content; }

    /**
     * Assigns contents to the contained value.
     * Assigns by copying the state of rhs, as if by any(rhs).swap(*this).
     *
     * @param rhs object whose contained value to assign
     */
    any &operator=(const any &rhs)
    {
        any(rhs).swap(*this);
        return *this;
    }

    /**
     * Assigns contents to the contained value.
     * Assigns by moving the state of rhs, as if by any(std::move(rhs)).swap(*this).
     * rhs is left in a valid but unspecified state after the assignment.
     *
     * @param rhs object whose contained value to assign
     */
    any &operator=(any &&rhs) noexcept
    {
        rhs.swap(*this);
        any().swap(rhs);
        return *this;
    }

    /**
     * Assigns contents to the contained value.
     * Assigns the type and value of rhs, as if by any(std::forward<ValueType>(rhs)).swap(*this).
     * This overload only participates in overload resolution if std::decay_t<ValueType> is not
     * the same type as any and std::is_copy_constructible_v<std::decay_t<ValueType>> is true.
     *
     * @param rhs object whose contained value to assign
     */
    template<class ValueType>
    any &operator=(ValueType &&rhs)
    {
        any(static_cast<ValueType &&>(rhs)).swap(*this);
        return *this;
    }

    /**
     * If not empty, destroys the contained object.
     */
    void reset() noexcept { any().swap(*this); }

    /**
     * Swaps the content of two any objects.
     *
     * @param other object to swap with
     */
    any &swap(any &rhs) noexcept
    {
        std::swap(content, rhs.content);
        return *this;
    }

    /**
     * Checks whether the object contains a value.
     *
     * @return true if instance contains a value, otherwise false.
     */
    bool has_value() const noexcept { return content; }

    /**
     * Queries the contained type.
     *
     * The typeid of the contained value if instance is non-empty, otherwise typeid(void).
     */
    const std::type_info &type() const noexcept { return content ? content->type() : typeid(void); }

private:
    class placeholder {
    public:
        virtual ~placeholder() {}

    public:
        virtual const std::type_info &type() const noexcept = 0;

        virtual placeholder *clone() const = 0;
    };

    template<typename ValueType>
    class holder : public placeholder {
    public:
        holder(const ValueType &value) : held(value) {}

        holder(ValueType &&value) : held(static_cast<ValueType &&>(value)) {}

        virtual const std::type_info &type() const noexcept { return typeid(ValueType); }

        virtual placeholder *clone() const { return new holder(held); }

        ValueType held;

    private:
        holder &operator=(const holder &);
    };

private:
    template<typename ValueType>
    friend ValueType *any_cast(any *) noexcept;

    placeholder *content;
};

/**
 * Overloads the std::swap algorithm for std::any. Swaps the content of two any objects by calling lhs.swap(rhs).
 *
 * @param lhs objects to swap
 * @param rhs objects to swap
 */
inline void
swap(any &lhs, any &rhs) noexcept
{
    lhs.swap(rhs);
}

/**
 * Defines a type of object to be thrown by the value-returning forms of libanyboost::any_cast on failure.
 */
class bad_any_cast : public std::bad_cast {
public:
    /**
     * Returns the explanatory string.
     *
     * Pointer to a null-terminated string with explanatory information. The pointer is guaranteed to be
     * valid at least until the exception object from which it is obtained is destroyed, or until a
     * non-const member function on the exception object is called.
     */
    virtual const char *what() const noexcept override { return "bad any_cast"; }
};

/**
 * Performs type-safe access to the contained object.
 *
 * Throws libanyboost::bad_any_cast if the typeid of the requested
 * ValueType does not match that of the contents of operand.
 *
 * @param operand target any object
 */
template<typename ValueType>
ValueType *
any_cast(any *operand) noexcept
{
    return operand && operand->type() == typeid(ValueType)
        ? std::addressof(
            static_cast<any::holder<typename std::remove_cv<ValueType>::type> *>(operand->content)
                ->held)
        : 0;
}

/**
 * Performs type-safe access to the contained object.
 *
 * Throws libanyboost::bad_any_cast if the typeid of the requested
 * ValueType does not match that of the contents of operand.
 *
 * @param operand target any object
 */
template<typename ValueType>
inline const ValueType *
any_cast(const any *operand) noexcept
{
    return any_cast<ValueType>(const_cast<any *>(operand));
}

/**
 * Performs type-safe access to the contained object.
 *
 * Throws libanyboost::bad_any_cast if the typeid of the requested
 * ValueType does not match that of the contents of operand.
 *
 * @param operand target any object
 */
template<typename ValueType>
ValueType
any_cast(any &operand)
{
    typedef typename std::remove_reference<ValueType>::type nonref;

    nonref *result = any_cast<nonref>(std::addressof(operand));
    if (!result) throw bad_any_cast();

    typedef typename std::conditional<std::is_reference<ValueType>::value,
                                      ValueType,
                                      typename std::add_lvalue_reference<ValueType>::type>::type
        ref_type;

    return static_cast<ref_type>(*result);
}

/**
 * Performs type-safe access to the contained object.
 *
 * Throws libanyboost::bad_any_cast if the typeid of the requested
 * ValueType does not match that of the contents of operand.
 *
 * @param operand target any object
 */
template<typename ValueType>
inline ValueType
any_cast(const any &operand)
{
    typedef typename std::remove_reference<ValueType>::type nonref;
    return any_cast<const nonref &>(const_cast<any &>(operand));
}

/**
 * Performs type-safe access to the contained object.
 *
 * Throws libanyboost::bad_any_cast if the typeid of the requested
 * ValueType does not match that of the contents of operand.
 *
 * @param operand target any object
 */
template<typename ValueType>
inline ValueType
any_cast(any &&operand)
{
    static_assert(std::is_rvalue_reference<ValueType &&>::value
                      || std::is_const<typename std::remove_reference<ValueType>::type>::value,
                  "any_cast shall not be used for getting nonconst references to "
                  "temporary objects");

    return any_cast<ValueType>(operand);
}

}// namespace reflection

}// namespace meta

#endif /* META_ANY_H */