How to recreate a vector without unnecessary copies in c++?

@lonzo 

To recreate a vector without unnecessary copies in C++, you can use constructs like move semantics and emplace functions. Here's an example on how to achieve this:

1. Move Semantics: Instead of creating unnecessary copies, move semantics allow you to transfer the ownership of resources from one object to another.

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std::vector<int> originalVector = {1, 2, 3}; // Or any other vector

// Copy the original vector with move semantics
std::vector<int> newVector = std::move(originalVector);

In this example, std::move is used to transfer the contents of originalVector to newVector efficiently, without making unnecessary copies. After this operation, originalVector is in a valid but unspecified state.

1. Emplace Functions: Instead of first creating an object and then copying it to the vector, emplace functions directly construct the object inside the vector, avoiding the need for intermediate copies.

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std::vector<std::pair<int, std::string>> vectorPairs;

// Instead of creating a temporary pair and then copying it to the vector,
// emplace a new pair directly into the vector
vectorPairs.emplace_back(1, "one");
vectorPairs.emplace_back(2, "two");

In this example, emplace_back constructs the std::pair directly inside the vectorPairs vector, avoiding copies.

By using move semantics and emplace functions, you can avoid unnecessary copies when recreating or populating vectors in C++.

@lonzo 

Another approach to recreate a vector without unnecessary copies in C++ is to use the std::swap function. std::swap exchanges the contents of two objects efficiently without making unnecessary copies.

Here is an example showcasing the use of std::swap in recreating a vector:

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std::vector<int> originalVector = {1, 2, 3}; // Original vector
std::vector<int> newVector; // New vector

// Clear the new vector and swap its contents with the original vector
newVector.clear();
std::swap(originalVector, newVector);

// Now the new vector contains the elements of the original vector efficiently

In this example, std::swap is used to exchange the contents of originalVector with newVector, effectively transferring the ownership of the vector contents without creating unnecessary copies.

Using std::swap can be a useful technique in cases where you want to efficiently recreate a vector without the overhead of unnecessary copies.