scope.h

 
#pragma once
 
#include "min-cpp-version/cpp17.h"
#include <type_traits>
#include <utility>
 
namespace ghassanpl
{

    template <class EF>
    struct scope_guard
    {
        template <class EFP>
        explicit scope_guard(EFP&& f) noexcept(noexcept(EFP(std::forward<EFP>(f))))
            : exit_function(std::forward<EFP>(f))
        {
        }
 
        scope_guard(scope_guard&& rhs) noexcept(noexcept(EF(std::move(rhs.exit_function))))
            : exit_function(std::move(rhs.exit_function))
        {
            rhs.release();
        }
 
        scope_guard(const scope_guard&) = delete;
        scope_guard& operator=(const scope_guard&) = delete;
        scope_guard& operator=(scope_guard&&) = delete;
 
        ~scope_guard() noexcept(noexcept(this->exit_function()))
        {
            if (this->execute_on_destruction)
                this->exit_function();
        }
 
        void release() noexcept
        {
            this->execute_on_destruction = false;
        }
 
        bool will_execute_on_destruction() const noexcept
        {
            return this->execute_on_destruction;
        }
 
    private:
 
        EF exit_function;
        bool execute_on_destruction{ true };
    };

    template <class EF>
    struct counted_scope_guard
    {
        template <class EFP>
        explicit counted_scope_guard(EFP&& f, int initial_count = 0) noexcept(noexcept(EFP(std::forward<EFP>(f))))
            : m_exit_function(std::forward<EFP>(f))
            , m_count(initial_count)
        {
        }
 
        counted_scope_guard(counted_scope_guard&& rhs) noexcept(noexcept(EF(std::move(rhs.m_exit_function))))
            : m_exit_function(std::move(rhs.m_exit_function))
            , m_count(std::exchange(rhs.m_count, 0))
        {
        }
 
        counted_scope_guard(const counted_scope_guard&) = delete;
        counted_scope_guard& operator=(const counted_scope_guard&) = delete;
        counted_scope_guard& operator=(counted_scope_guard&&) = delete;

        ~counted_scope_guard() noexcept(noexcept(m_exit_function()))
        {
            if (m_count > 0)
                m_exit_function();
        }

        void request() noexcept
        {
            ++m_count;
        }

        void unrequest() noexcept
        {
            if (m_count > 0)
                --m_count;
        }

        void release() noexcept
        {
            m_count = 0;
        }
 
        bool will_execute_on_destruction() const noexcept
        {
            return m_count > 0;
        }
 
    private:
 
        EF m_exit_function;
        int m_count = 0;
    };
 
    template <class EF>
    scope_guard(EF) -> scope_guard<EF>;

    template <class R, class D> 
    struct unique_resource
    {
        unique_resource() = default;
 
        template <class RR, class DD>
        unique_resource(RR&& r, DD&& d) noexcept(std::is_nothrow_constructible_v<R1, RR> && std::is_nothrow_constructible_v<D, DD>)
            : resource(std::forward<RR>(r))
            , deleter(std::forward<DD>(d))
            , execute_on_reset(true)
        {
        }
 
        template <class RR, class DD, class I = std::decay_t<RR>>
        unique_resource(RR&& r, const I& invalid, DD&& d) noexcept(std::is_nothrow_constructible_v<R1, RR> && std::is_nothrow_constructible_v<D, DD>)
            : resource(std::forward<RR>(r))
            , deleter(std::forward<DD>(d))
            , execute_on_reset(!bool(resource == invalid))
        {
        }
 
        unique_resource(unique_resource&& rhs) noexcept(std::is_nothrow_move_constructible_v<R1> && std::is_nothrow_move_constructible_v<D>)
            : resource(std::move(rhs.resource))
            , deleter(std::move(rhs.deleter))
            , execute_on_reset(std::exchange(rhs.execute_on_reset, false))
        {
        }
 
        ~unique_resource() noexcept(noexcept(deleter(resource)))
        {
            if (execute_on_reset)
                deleter(resource);
        }
 
        unique_resource& operator=(unique_resource&& rhs) noexcept(std::is_nothrow_move_assignable_v<R1> && std::is_nothrow_move_assignable_v<D> && noexcept(deleter(resource)))
        {
            if (std::addressof(rhs) == this)
                return *this;
 
            reset();
            if constexpr (std::is_nothrow_move_assignable_v<R1>)
            {
                if constexpr (std::is_nothrow_move_assignable_v<D>)
                {
                    resource = std::move(rhs.resource);
                    deleter = std::move(rhs.deleter);
                }
                else
                {
                    deleter = rhs.deleter;
                    resource = std::move(rhs.resource);
                }
            }
            else
            {
                if constexpr (std::is_nothrow_move_assignable_v<D>)
                {
                    resource = rhs.resource;
                    deleter = std::move(rhs.deleter);
                }
                else
                {
                    resource = rhs.resource;
                    deleter = rhs.deleter;
                }
            }
            execute_on_reset = std::exchange(rhs.execute_on_reset, false);
            return *this;
        }
 
        void reset() noexcept(noexcept(deleter(resource)))
        {
            if (execute_on_reset)
            {
                execute_on_reset = false;
                deleter(resource);
            }
        }
 
        template <class RR>
        void reset(RR&& r) noexcept(noexcept(deleter(resource)) && std::is_nothrow_assignable_v<R1&, RR>)
        {
            if (std::addressof(r) == std::addressof(resource))
                return;
 
            reset();
            try
            {
                if constexpr (std::is_nothrow_assignable_v<R1&, RR>)
                    resource = std::forward<RR>(r);
                else
                    resource = std::as_const(r);
            }
            catch (...)
            {
                deleter(r);
                throw;
            }
            execute_on_reset = true;
        }
 
        void release() noexcept
        {
            execute_on_reset = false;
        }
 
        const R& get() const noexcept
        {
            return resource;
        }
        explicit operator R&() noexcept { return resource; }
 
        auto operator*() const noexcept
        GHPL_REQUIRES(std::is_pointer_v<R> && (!std::is_void_v<std::remove_pointer_t<R>>))
        {
            return *get();
        }
 
        R operator->() const noexcept
        GHPL_REQUIRES(std::is_pointer_v<R>)
        {
            return get();
        }
 
        const D& get_deleter() const noexcept { return deleter; }
 
    private:
 
        using R1 = std::conditional_t<std::is_reference_v<R>, std::reference_wrapper<std::remove_reference_t<R>>, R>;
        R1 resource{};
        D deleter{};
        bool execute_on_reset{};
    };
 
    template<class R, class D>
    unique_resource(R, D) -> unique_resource<R, D>;
    template <class R, class D, class I = std::decay_t<R>>
    unique_resource(R, I, D) -> unique_resource<R, D>;

    template <typename T, bool IS_OPTIONAL = false>
    struct scoped_value_change
    {
        template <typename U, bool OPT = IS_OPTIONAL>
        scoped_value_change(T& ref, U new_val, typename std::enable_if_t<!OPT>* = 0) noexcept(std::is_nothrow_move_constructible_v<T>)
            : m_ref(std::addressof(ref))
            , m_original_value(std::exchange(ref, new_val))
        {
        }
 
        template <typename U, bool OPT = IS_OPTIONAL>
        scoped_value_change(T& ref, U new_val, typename std::enable_if_t<OPT>* = 0) noexcept(std::is_nothrow_move_constructible_v<T> && std::is_nothrow_copy_constructible_v<T>)
            : m_ref(std::addressof(ref))
            , m_original_value(*m_ref != new_val ? std::exchange(ref, new_val) : ref)
        {
        }
 
        ~scoped_value_change() noexcept(std::is_nothrow_move_assignable_v<T>)
        {
            revert();
        }
 
        scoped_value_change(const scoped_value_change&) = delete;
        scoped_value_change(scoped_value_change&& other) noexcept(std::is_nothrow_move_constructible_v<T>)
            : m_ref(other.m_ref)
            , m_original_value(std::move(other.m_original_value))
        {
            other.m_ref = nullptr;
        }
 
        scoped_value_change& operator=(const scoped_value_change&) = delete;

        scoped_value_change& operator=(scoped_value_change&& other) = delete;
 
        /*
        scoped_value_change& operator=(scoped_value_change&& other) noexcept(std::is_nothrow_move_assignable_v<T>)
        {
            revert();
 
            m_ref = other.m_ref;
            m_original_value = std::move(other.m_original_value);
            other.m_ref = nullptr;
            return *this;
        }
        */
 
        bool valid() const noexcept { return m_ref != nullptr; }

        T const& original_value() const & noexcept
        {
            return m_original_value;
        }

        T original_value() && noexcept(std::is_nothrow_move_constructible_v<T>)
        {
            return std::move(m_original_value);
        }

        T const& current_value()
        {
            return *m_ref;
        }

        void revert() noexcept(std::is_nothrow_move_assignable_v<T>)
        {
            if (m_ref)
            {
                auto& ref = *m_ref;
                m_ref = nullptr;
 
                if constexpr (IS_OPTIONAL)
                {
                    if (ref == m_original_value)
                        return;
                }
                
                ref = std::move(m_original_value);
            }
        }

        T revert_and_return() noexcept(std::is_nothrow_move_assignable_v<T> && std::is_nothrow_move_constructible_v<T>)
        {
            auto& ref = *m_ref;
            m_ref = nullptr;
 
            if constexpr (IS_OPTIONAL)
            {
                if (ref != m_original_value)
                    return std::move(m_original_value);
            }
 
            return std::exchange(ref, std::move(m_original_value));
        }

        void release() noexcept
        {
            m_ref = nullptr;
        }

        T release_and_return() noexcept(std::is_nothrow_move_constructible_v<T>)
        {
            m_ref = nullptr;
            return std::move(m_original_value);
        }
 
    private:
 
        T* m_ref;
        T m_original_value;
    };
 
    template <typename T>
    using optional_scoped_value_change = scoped_value_change<T, true>;
 
    template <typename T, typename U>
    scoped_value_change(T&, U&&) -> scoped_value_change<T>;
 
    // TODO: atomic_scoped_value_change
    
    template <typename T>
    struct scope_counter
    {
        scope_counter(T& ref) noexcept(noexcept(++ref))
            : m_ref(std::addressof(ref))
        {
            ++ref;
        }
 
        scope_counter(const scope_counter&) = delete;
        scope_counter(scope_counter&& other) noexcept
        {
            m_ref = std::exchange(other.m_ref, nullptr);
        }
        scope_counter& operator=(const scope_counter&) = delete;
        scope_counter& operator=(scope_counter&&) = delete;
 
        bool valid() const noexcept { return m_ref != nullptr; }
 
        ~scope_counter() noexcept(noexcept(--m_ref))
        {
            if (m_ref)
                --m_ref;
        }
 
        void release() const noexcept
        {
            m_ref = nullptr;
        }
 
    private:
 
        T* m_ref;
    };
 

}