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Questions tagged [copy-and-swap]

The copy swap idiom in C++ can be used to simplify the implementation of the assignment operator by used the copy constructor to generate a local copy and swapping it with the current object.

The copy swap idiom in C++ can be used to simplify the implementation of the assignment operator by used the copy constructor to generate a local copy and swapping it with the current object.

Use this tag for questions related to the copy and swap idiom.

For more detail, see also this Stackoverflow question.

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Safe assignment and copy-and-swap idiom

I'm learning c++ and I recently learned (here in stack overflow) about the copy-and-swap idiom and I have a few questions about it. So, suppose I have the following class using a copy-and-swap idiom, just for example: class Foo { private: int *…
Rafael S. Calsaverini
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ambiguous overload for ‘operator=’ with c++11 std::move and copy and swap idiom

I am getting the following error: [matt ~] g++ -std=c++11 main.cpp -DCOPY_AND_SWAP && ./a.out main.cpp: In function ‘int main(int, const char* const*)’: main.cpp:101:24: error: ambiguous overload for ‘operator=’ in ‘move = std::move((* &…
Matt Clarkson
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Does it make sense to use the move-and-swap idiom on a movable and non-copyable class

If I have a class such as class Foo{ public: Foo(){...} Foo(Foo && rhs){...} operator=(Foo rhs){ swap(*this, rhs);} void swap(Foo &rhs); private: Foo(const Foo&); // snip: swap code }; void swap(Foo& lhs, Foo& rhs); Does it make…
Flame
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copy and swap idiom with pure virtual class

I am trying to implement virtual class with pure virtual method and 'copy and swap' idiom, but I've encountered some problems. Code won't compile because I am creating instance in the assign operator of the class A which contains pure virtual…
Rob
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Assignment via copy-and-swap vs two locks

Borrowing Howard Hinnant's example and modifying it to use copy-and-swap, is this op= thread-safe? struct A { A() = default; A(A const &x); // Assume implements correct locking and copying. A& operator=(A x) { std::lock_guard…
Fred Nurk
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Why SGI STL don't use the copy-and-swap idiom?

I recently read an answer on StackOverflow about What is the copy-and-swap idiom? and knew that the copy-and-swap idiom can avoiding code duplication, and providing a strong exception guarantee. However, when I looked into SGI STL deque…
abcdabcd987
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What is the proper approach to swap and copy idiom in virtual inheritance?

Consider classic virtual inheritance diamond hierarchy. I wonder to know what is the right implementation of copy and swap idiom in such hierarchy. The example is a little artificial - and it is not very smart - as it would play good with default…
PiotrNycz
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How do I swap an MFC CString?

OK, so I'm all sold on the copy-and-swap idiom and I think I mostly know how to implement it. However, or codebase uses MFC's CString class as string and this ain't gonna change. Since swap must (should???) be nothrow, I cannot…
Martin Ba
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linking error in friend function of a template class

I have template class node and in order to follow the copy-and-swap idiom i am tryig to write the swap function which is a friend of class Node my code is : Node.h #ifndef NODE_H #define NODE_H #include template class Node { …
Hummingbird
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Is it OK to have a throwing swap member-implementation?

The general guideline when writing classes (using the copy-and-swap idiom) is to provide a non throwing swap member function. (Effective C++, 3rd edition, Item 25 and other resources) However, what if I cannot provide the nothrow guarantee because…
Martin Ba
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Implementing the swap in the copy and swap idiom

Following What is the copy and swap idiom and How to provide a swap function for my class, I tried implementing the swap function like in the latter accepted answer option number 2 (having a free function that calls a member function) instead of the…
green diod
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Copy-and-swap done through interfaces

I'm trying to implement a copy+swap idiom to achieve strong-exception safety through a level of abstraction and, although the principle is clear, as it's often the case the devil is in the detail. Say I have a class that looks like this: class…
Alberto Giannetto
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Lock-free Shared Memory in C++ for Variable length Records

I am newbee to IPC. The Writer process writes the data into shared memory, Many reader processes reads the data. The data to be written have a unique identifier, has to be be indexed by unique key for the faster access( like STL::map or hashmap for…
naveenhegde
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Copy-and-Swap idiom for class with references to abstract classes

I'm trying to implement the Copy-and-Swap Idiom for my class, because I need to implement operator=, and since it has reference members, and references can only be assigned once, I thought that the aforementioned idiom was a valid workaround. But…
dario_ramos
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Unresolved external using template class with copy-and-swap

I'm getting a linker error when using a template class where I tried implementing the copy-and-swap idiom as suggested here: What is the copy-and-swap idiom? The template class, let's call it "TemplateClass" is partially defined like this: template<…
Tim Meyer
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