shared_ptr.h

// Source: https://github.com/X-czh/smart_ptr
// SPDX-License-Identifier: MIT
//
// This file has been modified by Adobe.
//
// All modifications are Copyright 2022 Adobe.
 
#pragma once
 
#include <lagrange/internal/smart_ptr/control_block.h>
#include <lagrange/internal/weak_ptr.h>
 
#include <cstddef> 
#include <iostream> 
#include <memory> 
#include <type_traits> 
#include <utility> 
 
namespace lagrange::internal {
 
// Forward declarations
 
template <typename T>
class shared_ptr;
template <typename T>
class weak_ptr;
 
// shared_ptr_access general template
// Defines operator*, operator-> and operator[]
// for T not array or cv void
 
template <typename T, bool = std::is_array<T>::value, bool = std::is_void<T>::value>
class shared_ptr_access
{
public:
    using element_type = T;
 
    element_type& operator*() const noexcept
    {
        assert(_get() != nullptr);
        return *_get();
    }
 
    element_type* operator->() const noexcept
    {
        assert(_get() != nullptr);
        return _get();
    }
 
private:
    element_type* _get() const noexcept { return static_cast<const shared_ptr<T>*>(this)->get(); }
};
 
// specialization of shared_ptr_access for T array type
// Defines operator[] for shared_ptr<T[]> and shared_ptr<T[N]>
 
template <typename T>
class shared_ptr_access<T, true, false>
{
public:
    using element_type = typename std::remove_extent<T>::type;
 
    element_type* operator[](std::ptrdiff_t i) const noexcept
    {
        assert(_get() != nullptr);
        static_assert(!std::extent<T>::value || i < std::extent<T>::value);
        return _get()[i];
    }
 
private:
    element_type* _get() const noexcept { return static_cast<const shared_ptr<T>*>(this)->get(); }
};
 
// specialization of shared_ptr_access for T cv void type
// Defines operator-> for shared_ptr<cv void>
 
template <typename T>
class shared_ptr_access<T, false, true>
{
public:
    using element_type = T;
 
    element_type* operator->() const noexcept
    {
        assert(_get() != nullptr);
        return _get();
    }
 
private:
    element_type* _get() const noexcept { return static_cast<const shared_ptr<T>*>(this)->get(); }
};
 
// 20.7.2.2 Class template shared_ptr
 
/* supports shared_ptr<T[]> and shared_ptr<T[N]>: added in C++17 */
 
template <typename T>
class shared_ptr : public shared_ptr_access<T>
{
public:
    template <typename U>
    friend class shared_ptr;
 
    template <typename U>
    friend class weak_ptr;
 
    using element_type = typename shared_ptr_access<T>::element_type;
    using weak_type = weak_ptr<T>; /* added in C++17 */
 
    // 20.7.2.2.1, constructors
 
    constexpr shared_ptr() noexcept
        : _ptr{}
        , _control_block{}
    {}
 
    constexpr shared_ptr(std::nullptr_t) noexcept
        : _ptr{}
        , _control_block{}
    {}
 
    template <typename U>
    explicit shared_ptr(U* p)
        : _ptr{p}
        , _control_block{new control_block<U>{p}}
    {}
 
    template <typename U, typename D, typename A>
    shared_ptr(U* p, D d, A a) = delete;
 
    template <typename D, typename A>
    shared_ptr(std::nullptr_t p, D d, A a) = delete;
 
    template <typename U>
    shared_ptr(const shared_ptr<U>& sp, T* p) noexcept
        : _ptr{p}
        , _control_block{sp._control_block}
    {
        if (_control_block) _control_block->inc_ref();
    }
 
    shared_ptr(const shared_ptr& sp) noexcept
        : _ptr{sp._ptr}
        , _control_block{sp._control_block}
    {
        if (_control_block) _control_block->inc_ref();
    }
 
    template <typename U>
    shared_ptr(const shared_ptr<U>& sp) noexcept
        : _ptr{sp._ptr}
        , _control_block{sp._control_block}
    {
        if (_control_block) _control_block->inc_ref();
    }
 
    shared_ptr(shared_ptr&& sp) noexcept
        : _ptr{std::move(sp._ptr)}
        , _control_block{std::move(sp._control_block)}
    {
        sp._ptr = nullptr;
        sp._control_block = nullptr;
    }
 
    template <typename U>
    shared_ptr(shared_ptr<U>&& sp) noexcept
        : _ptr{sp._ptr}
        , _control_block{sp._control_block}
    {
        sp._ptr = nullptr;
        sp._control_block = nullptr;
    }
 
    template <typename U>
    explicit shared_ptr(const weak_ptr<U>& wp)
        : _ptr{wp._ptr}
        , _control_block{wp._control_block}
    {
        if (wp.expired()) {
            throw std::bad_weak_ptr{};
        } else {
            _control_block->inc_ref();
        }
    }
 
    // 20.7.2.2.2, destructor
 
    ~shared_ptr()
    {
        if (_control_block) _control_block->dec_ref();
    }
 
    // 20.7.2.2.3, assignment
 
    shared_ptr& operator=(const shared_ptr& sp) noexcept
    {
        shared_ptr{sp}.swap(*this);
        return *this;
    }
 
    template <typename U>
    shared_ptr& operator=(const shared_ptr<U>& sp) noexcept
    {
        shared_ptr{sp}.swap(*this);
        return *this;
    }
 
    shared_ptr& operator=(shared_ptr&& sp) noexcept
    {
        shared_ptr{std::move(sp)}.swap(*this);
        return *this;
    }
 
    template <typename U>
    shared_ptr& operator=(shared_ptr<U>&& sp) noexcept
    {
        shared_ptr{std::move(sp)}.swap(*this);
        return *this;
    }
 
    // 20.7.2.2.4, modifiers
 
    void swap(shared_ptr& sp) noexcept
    {
        using std::swap;
        swap(_ptr, sp._ptr);
        swap(_control_block, sp._control_block);
    }
 
    void reset() noexcept { shared_ptr{}.swap(*this); }
 
    template <typename U>
    void reset(U* p)
    {
        shared_ptr{p}.swap(*this);
    }
 
    template <typename U, typename D>
    void reset(U* p, D d)
    {
        shared_ptr{p, d}.swap(*this);
    }
 
    template <typename U, typename D, typename A>
    void reset(U* p, D d, A a) = delete;
 
    // 20.7.2.2.5, observers
 
    element_type* get() const noexcept { return _ptr; }
 
    /* implemented in shared_ptr_access<T> */
 
    // /// Dereferences pointer to the managed object
    // element_type&
    // operator*() const noexcept
    // { return *_ptr; }
 
    // /// Dereferences pointer to the managed object
    // element_type*
    // operator->() const noexcept
    // { return _ptr; }
 
    long use_count() const noexcept { return (_control_block) ? _control_block->use_count() : 0; }
 
    /* deprecated in C++17, removed in C++20 */
    bool unique() const noexcept { return (_control_block) ? _control_block->unique() : false; }
 
    explicit operator bool() const noexcept { return (_ptr) ? true : false; }
 
private:
    element_type* _ptr;
    control_block_base* _control_block;
};
 
// 20.7.2.2.6, shared_ptr creation
 
template <typename T, typename... Args>
inline shared_ptr<T> make_shared(Args&&... args)
{
    return shared_ptr<T>{new T{std::forward<Args>(args)...}};
}
 
template <typename T, typename A, typename... Args>
inline shared_ptr<T> allocate_shared(const A& a, Args&&... args) = delete;
 
// 20.7.2.2.7, shared_ptr comparisons
 
template <typename T, typename U>
inline bool operator==(const shared_ptr<T>& sp1, const shared_ptr<U>& sp2)
{
    return sp1.get() == sp2.get();
}
 
template <typename T>
inline bool operator==(const shared_ptr<T>& sp, std::nullptr_t) noexcept
{
    return !sp;
}
 
template <typename T>
inline bool operator==(std::nullptr_t, const shared_ptr<T>& sp) noexcept
{
    return !sp;
}
 
template <typename T, typename U>
inline bool operator!=(const shared_ptr<T>& sp1, const shared_ptr<U>& sp2)
{
    return sp1.get() != sp2.get();
}
 
template <typename T>
inline bool operator!=(const shared_ptr<T>& sp, std::nullptr_t) noexcept
{
    return bool{sp};
}
 
template <typename T>
inline bool operator!=(std::nullptr_t, const shared_ptr<T>& sp) noexcept
{
    return bool{sp};
}
 
// 20.7.2.2.8, shared_ptr specialized algorithms
 
template <typename T>
inline void swap(shared_ptr<T>& sp1, shared_ptr<T>& sp2)
{
    sp1.swap(sp2);
}
 
// 20.7.2.2.9, shared_ptr casts
 
template <typename T, typename U>
inline shared_ptr<T> static_pointer_cast(const shared_ptr<U>& sp) noexcept
{
    using _Sp = shared_ptr<T>;
    return _Sp(sp, static_cast<typename _Sp::element_type*>(sp.get()));
}
 
template <typename T, typename U>
inline shared_ptr<T> const_pointer_cast(const shared_ptr<U>& sp) noexcept
{
    using _Sp = shared_ptr<T>;
    return _Sp(sp, const_cast<typename _Sp::element_type*>(sp.get()));
}
 
template <typename T, typename U>
inline shared_ptr<T> dynamic_pointer_cast(const shared_ptr<U>& sp) noexcept
{
    using _Sp = shared_ptr<T>;
    if (auto* _p = dynamic_cast<typename _Sp::element_type*>(sp.get())) return _Sp(sp, _p);
    return _Sp();
}
 
/* added in C++17 */
template <typename T, typename U>
inline shared_ptr<T> reinterpret_pointer_cast(const shared_ptr<U>& sp) noexcept
{
    using _Sp = shared_ptr<T>;
    return _Sp(sp, reinterpret_cast<typename _Sp::element_type*>(sp.get()));
}
 
// 20.7.2.2.11, shared_ptr I/O
 
template <class E, class T, class Y>
inline std::basic_ostream<E, T>& operator<<(std::basic_ostream<E, T>& os, const shared_ptr<Y>& sp)
{
    os << sp.get();
    return os;
}
 
} // namespace lagrange::internal