pimpl.h

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/*  Copyright (c) SILVERCODERS Ltd, http://silvercoders.com                                                                                  */
/*  Project homepage: https://github.com/docwire/docwire                                                                                     */
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/*  SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-DocWire-Commercial                                                                  */
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#ifndef DOCWIRE_PIMPL_H
#define DOCWIRE_PIMPL_H
 
#include <memory>
 
namespace docwire
{
 
template <typename T>
struct pimpl_impl;
 
class with_pimpl_base {};
 
struct pimpl_impl_base
{
    virtual ~pimpl_impl_base() = default;
    virtual void set_owner(with_pimpl_base&)
    {
    }
};
 
template <typename T>
class with_pimpl_owner;
 
template <typename T>
class with_pimpl : public with_pimpl_base
{
protected:
    using impl_type = pimpl_impl<T>;
 
    template <typename... Args>
    impl_type* create_impl(Args&&... args)
    {
        if constexpr (std::is_base_of_v<with_pimpl_owner<T>, impl_type>)
        {
            static_assert(std::is_constructible_v<impl_type, T&, Args...>,
                "Template specialization of pimpl_impl<T> that inherits from with_pimpl_owner<T> is required to have constructor with T&, Args... arguments");
            return new impl_type(static_cast<T&>(*this), std::forward<Args>(args)...);
        }
        else
        {
            static_assert(std::is_constructible_v<impl_type, Args...>,
                "Template specialization of pimpl_impl<T> is required to have constructor with Args... arguments");
            return new impl_type(std::forward<Args>(args)...);
        }
    }
 
    template <typename... Args>
    explicit with_pimpl(Args&&... args)
        : m_impl(static_cast<pimpl_impl_base*>(create_impl(std::forward<Args>(args)...)))
    {
    }
 
    with_pimpl(with_pimpl<T>&& other) noexcept
        : m_impl(std::move(other.m_impl))
    {
        if (m_impl)
            set_impl_owner();
    }
 
    with_pimpl(std::nullptr_t) {}
 
    with_pimpl& operator=(with_pimpl&& other) noexcept {
        if (this != &other)
        {
            m_impl = std::move(other.m_impl);
            if (m_impl)
                set_impl_owner();
        }
        return *this;
    }
 
    template <typename DeferInstantiation = void>
    impl_type& impl() { return *static_cast<impl_type*>(m_impl.get()); }
 
    template <typename DeferInstantiation = void>
    const impl_type& impl() const { return *static_cast<impl_type*>(m_impl.get()); }
 
private:
    std::unique_ptr<pimpl_impl_base> m_impl;
 
    void set_impl_owner()
    {
        m_impl->set_owner(*this);
    }
};
 
template <typename T>
class with_pimpl_owner : public pimpl_impl_base
{
protected:
    with_pimpl_owner(T& owner) : m_owner(owner) {}
    T& owner() { return m_owner; }
    const T& owner() const { return m_owner; }
 
    void set_owner(with_pimpl_base& owner) override
    {
        m_owner = static_cast<T&>(static_cast<with_pimpl<T>&>(owner));
    }
 
private:
    std::reference_wrapper<T> m_owner;
    friend with_pimpl<T>;
};
 
} // namespace docwire
 
#endif