C++ Internals

std::shared_ptr and std::weak_ptr

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Language: C++23SharedPtr

#include <cstddef>
#include <type_traits>
#include <utility>

// ...
struct TestResource {
    inline static long long constructed = 0;
    inline static long long destroyed = 0;
    long long value;
    explicit TestResource(long long v) : value(v) { ++constructed; }
    ~TestResource() { ++destroyed; }
    static void reset() {
        constructed = 0;
        destroyed = 0;
    }
};

// ...
// ...
// ...
struct ControlBlock {
    // ...
    // ...
    inline static long long created = 0;
    inline static long long freed = 0;
    ControlBlock() { ++created; }
    ~ControlBlock() { ++freed; }
    static void reset() {
        created = 0;
        freed = 0;
    }

    long long strong = 1;
    long long weak = 0;
};

template <typename T>
class WeakPtr;

template <typename T>
class SharedPtr {
public:
    SharedPtr() noexcept = default;

    explicit SharedPtr(T* ptr) : ptr_(ptr) {
        // ...
    }

    ~SharedPtr() {
        // ...
    }

    // ...
    // ...

    void reset(T* ptr = nullptr) {
        // ...
        (void)ptr;
    }

    long long use_count() const {
        // ...
        return 0;
    }

    T* get() const noexcept { return ptr_; }
    T& operator*() const { return *ptr_; }
    T* operator->() const noexcept { return ptr_; }
    explicit operator bool() const noexcept { return ptr_ != nullptr; }

private:
    friend class WeakPtr<T>;

    T* ptr_ = nullptr;
    ControlBlock* block_ = nullptr;
};

template <typename T>
class WeakPtr {
public:
    WeakPtr() noexcept = default;

    WeakPtr(const SharedPtr<T>& owner) noexcept {
        // ...
        (void)owner;
    }

    ~WeakPtr() {
        // ...
    }

    // ...
    // ...

    void reset() noexcept {
        // ...
    }

    long long use_count() const noexcept {
        // ...
        return 0;
    }

    bool expired() const noexcept {
        // ...
        return true;
    }

    SharedPtr<T> lock() const {
        // ...
        return SharedPtr<T>();
    }

private:
    T* ptr_ = nullptr;
    ControlBlock* block_ = nullptr;
};

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