std::unique_ptr::reset(3)

hey bestie 💖 welcome to std::unique_ptr::reset(3), straight outta the C++ Standard Libary. this is the reset glow-up page — it replaces the managed object, and yes it's giving main character energy. no cap.

🎀 NAME 🎀

std::unique_ptr::reset — std::unique_ptr::reset

✨ Synopsis ✨

okay so here's the overload lineup, bestie — three of them, all noexcept, all constexpr since C++23:

members of the primary template, unique_ptr<T>
void reset( pointer ptr = pointer() ) noexcept;  (1) (constexpr since C++23)

members of the specialization unique_ptr<T[]>
template< class U >                              (2) (constexpr since C++23)
void reset( U ptr ) noexcept;
void reset( std::nullptr_t = nullptr ) noexcept; (3) (constexpr since C++23)

Replaces the managed object. periodt.

1. Given current_ptr, the pointer that was managed by *this, performs the following actions, in this order:
   1. Saves a copy of the current pointer: old_ptr = current_ptr.
   2. Overwrites the current pointer with the argument: current_ptr = ptr.
   3. If the old pointer was non-empty, deletes the previously managed object if (old_ptr) get_deleter()(old_ptr).
2. Behaves the same as the reset member of the primary template, except that it will only participate in overload resolution if either:
   1. U is the same type as pointer, or
   2. pointer is the same type as element_type* and U is a pointer type V* such that V(*)[] is convertible to element_type(*)[].
3. Equivalent to reset(pointer()).

🫶 Parameters 🫶

• ptr — pointer to a new object to manage

💖 Return value 💖

(none) — nothing comes back, bestie. it's giving silence.

🧠 Notes 🧠

• To replace the managed object while supplying a new deleter as well, the move assignment operator may be used.
• A test for self-reset — i.e. whether ptr points to an object already managed by *this — is not performed, except where provided as a compiler extension or as a debugging assert.
• Note that code such as p.reset(p.release()) does not involve self-reset, only code like p.reset(p.get()) does. 💀

🌸 Example 🌸

run this code, bestie:

// Run this code

#include <iostream>
#include <memory>

struct Foo // object to manage
{
    Foo() { std::cout << "Foo...\n"; }
    ~Foo() { std::cout << "~Foo...\n"; }
};

struct D // deleter
{
    void operator() (Foo* p)
    {
        std::cout << "Calling delete for Foo object... \n";
        delete p;
    }
};

int main()
{
    std::cout << "Creating new Foo...\n";
    std::unique_ptr<Foo, D> up(new Foo(), D()); // up owns the Foo pointer (deleter D)

    std::cout << "Replace owned Foo with a new Foo...\n";
    up.reset(new Foo());  // calls deleter for the old one

    std::cout << "Release and delete the owned Foo...\n";
    up.reset(nullptr);
}

🍓 Output 🍓

Creating new Foo...
Foo...
Replace owned Foo with a new Foo...
Foo...
Calling delete for Foo object...
~Foo...
Release and delete the owned Foo...
Calling delete for Foo object...
~Foo...

💅 Defect reports 💅

The following behavior-changing defect reports were applied retroactively to previously published C++ standards. slay for retroactive fixes ✨

• DR LWG 2118 — Applied to: C++11 — Behavior as published: unique_ptr<T[]>::reset rejected qualification conversions — Correct behavior: accepts.

👑 See also 👑

• release — returns a pointer to the managed object and releases the ownership (public member function)

source: http://cppreference.com — version/date: 2024.06.10 — page: std::unique_ptr::reset(3) — mwah 💋