C++ Internals

Smart Pointer From Scratch

Difficulty

Asked at Headlands Technologies

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"xxxxxxxxx xxxxxx_xxx" xx xxx xxxx-xxxxx x++ xxxxxx xxxxxxxx xx xxxxx-xxx xxxxxxxxxx, xxx xxx x xxxxxx: xx xxxxxx xxxxxxx xx xxxxxxx xxxxxxx xxx xxxxxxxxxx xxxxxxxxx, xxx xxxx xx xxxx, xxxxxxxx, xxx xxxxx xxx xxxxxxxxx xxxxx xxxxxxxx xxxxx. xxxxx xx xx xx x xxxxxxxx xxxx xxxx xx.

xxxxxxxxx xxxxxxxxx<x>, x xxxxxxxxx-xxxxxxx xxxxxx xxxxxxx. xxxxx xxx::xxxxxx_xxx xx xxx::xxxxxx_xxx xxxxxxxx xxxxxx xx xxxxxx; xxx xxxxxxx xxxxx xx xxx xxxxxxxx.

xxxxxxxxx(): xxxxx; xxx_xxxxx() == x, xxxxxxxx xxxx xxxxx.
xxxxxxxx xxxxxxxxx(x* xxx): xxxxx xxxxxxxxx xx xxx xxxx x xxxxx xx x. x xxxx xxx xxxxxxxx xx xxxxx xxxxxxxxx (xx xxxxxxx xxxxx).
xxxx xxxxxxxxxxx / xxxx xxxxxxxxxx: xxxxx xxxxxxxxx; xxx xxxxx xxxx xx xx xxx. xxxx xxxxxxxxxx xxxx xxxxxxx xxxx-xxxxxxxxxx (x = x) xxxxxxx xxxxxxxx xxx xxxxx xx xxxxxxxxxx xxxxxxxx.
xxxx xxxxxxxxxxx / xxxx xxxxxxxxxx: xxxxx xxxxxxxxx; xxx xxxxxx xx xxxx xxxxx. xx xxxxx xxxxxx.
xxxxxxxxxx xxxx xx xxxxxxxx xxxxxx xxxxx xxxxxxxx xxx xxxxxx'x xxxxxxx xxxxxxxxx (xxxxxxxxxx xxx xxxxxx xx xx xxx xxx xxxx).
~xxxxxxxxx(): xxxxxxxx xxx xxxxxxxxx; xxxxxxx xxxxx xxx xxxxx xx xxxx xxxxxxx xxx xxxxxx xxx xxx xxxxxxx xxxxx, xxxxxxx xxxx.
xxxx xxxxx(x* xxx = xxxxxxx): xxxxxxxx xxx xxxxxxx xxxxxxxxx, xxxx xxxx xxx xxxxx (xxxxx x) xx xxxxxxx xxxxx.
xxxx xxxx xxx_xxxxx() xxxxx: xxxxxxx xxxxx xxxxx; x xxxx xxxxx.
x& xxxxxxxx*() xxxxx, x* xxxxxxxx->() xxxxx, xxxxxxxx xxxxxxxx xxxx() xxxxx (xxxxxxxx xx xxx xxxxxxxx).

xxx xxxxxxxx xxxx xxxxxxxx xxxxxxxxxxxx, xx xxxxxxxxxxxx xxxxxxx xxxx xxxxxx xxxxxxxxxxx / xxxxxxxxx xxxxxxxx (xx xxx xxxxxx xx). xxx xxxxx xxxxx xxxxxxx xxxxxx, xxxx xxxx xxxx xx xxxxxxxxx xxxxxx, xxx xxxxx xxx xxxxxxxx: xxx xxxxxx xxxx xx xxxxxxxxx xxxxxxx xxxx, xxxxxxxxx xxxx xxx xxxx xxxxx xxxx xx, xxxxx xxxxxxx.

xxxxxxxx

[]{ xxxxxxxxxxxx::xxxxx(); xxx::xxxxxx<xxxx xxxx> xxx; { xxxxxxxxx<xxxxxxxxxxxx> x(xxx xxxxxxxxxxxx(x)); xxx.xxxx_xxxx(x->xxxxx); xxx.xxxx_xxxx(x.xxx_xxxxx()); xxx.xxxx_xxxx(xxxxxxxxxxxx::xxxxxxxxx); } xxx.xxxx_xxxx(xxxxxxxxxxxx::xxxxxxxxxxx); xxx.xxxx_xxxx(xxxxxxxxxxxx::xxxxxxxxx); xxxxxx xxx; }()
// [x, x, x, x, x]  (xxxxx xxxxxx xxx xxxxx, xxxxxxxxx xxxx xx xxxx)

[]{ xxxxxxxxxxxx::xxxxx(); xxx::xxxxxx<xxxx xxxx> xxx; { xxxxxxxxx<xxxxxxxxxxxx> x(xxx xxxxxxxxxxxx(x)); { xxxxxxxxx<xxxxxxxxxxxx> x(x); xxxxxxxxx<xxxxxxxxxxxx> x = x; xxx.xxxx_xxxx(x.xxx_xxxxx()); xxx.xxxx_xxxx(x->xxxxx); } xxx.xxxx_xxxx(x.xxx_xxxxx()); xxx.xxxx_xxxx(xxxxxxxxxxxx::xxxxxxxxx); } xxx.xxxx_xxxx(xxxxxxxxxxxx::xxxxxxxxx); xxxxxx xxx; }()
// [x, x, x, x, x]  (xxxxx xxxxxx; xxxxx xxxxxx xxxxxxx xxxx xxx xxxxxxx)

xxxxxxxxxxx

xxxxxx-xxxxxxxx: x xxxxx xxxxxxx xxxxx xx xxxxxxx xxxx (xxx xxxxxxxxx xxxxxx xxxx xxxxxxx xxxxx xxxxxx).
xx xxxxxxxxx xxxxxx xxxxxxxx: xxx/xxxxxx xxx xxx xxxxxx xxx xxx xxxxxxx xxxxx xxx xxxx.
xxx xxxxxx xxxxx xxxxx xxxx-xxxxxxxxxx, xxxx-xxxx-xxxxxxxx xxxxxxxx xxxxxxx xxxxx, xxxxx-xxxx xxxxx, xxx xxxxx xxxxxx xxxxxxxx xx xxxxxxxxx xxxxx. xxxxx xxxx xxxx xxxxx x xxxxxxxxx xxxx xx xxxxxxxx-xxxx: xxxxx xxxx xxxxx x = x xxxx xxxx xxxxx xxx xxxx xxxxxx.

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Language: C++SharedPtr

#include <cstddef>
#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; }
};

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

private:
    T* ptr_ = nullptr;
    // ...
};

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