push_back sv

`push_back` and `sv` are both features in C++.

`push_back` is a method available on many standard C++ containers such as `std::vector`, `std::deque`, and `std::list`. It is used to add an element to the end of the container.

For example, if we have a vector of integers:

std::vector<int> vec {1, 2, 3};

We can add an additional element to the end using `push_back`:

vec.push_back(4);

Now the vector contains `{1, 2, 3, 4}`.

`sv` on the other hand, is a C++20 feature that stands for "string view". It is used to create a read-only view of a string without copying its contents.

For example, if we have a string:

std::string str = "hello world";

We can create a string view of the first 5 characters using `sv`:

std::string_view view = str.substr(0, 5);

Now `view` contains `"hello"`, but does not copy the contents of `str`. This can be useful for passing strings around without incurring the cost of copying them.