C++ High Performance/

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Implementing a Simple Button Class with std::function

Implementing a Simple Button Class with std::function

Discover how to implement a Button class using std::function and its optimization.

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Using std::function to store actions in a Button class

Assume that we set out to implement a Button class. We can then use the std::function to store the action corresponding to clicking the button so that when we call the on_click() member function, the corresponding code is executed.

We can declare the Button class like this:

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class Button {
public:
  Button(std::function<void(void)> click) : handler_{click} {}
  auto on_click() const { handler_(); }
private:
  std::function<void(void)> handler_{};
};

We can then use it to create a multitude of buttons with different actions. The buttons can conveniently be stored in a container because they all have the same type:

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auto create_buttons () {
  auto beep = Button([counter = 0]() mutable {
    std::cout << "Beep:" << counter << "! ";
    ++counter;
  });
  auto bop = Button([] { std::cout << "Bop. "; });
  auto silent = Button([] {});
  return std::vector<Button>{beep, bop, silent};
}

Iterating the list and calling on_click() on each button will execute the corresponding function:

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C++
 const auto& buttons = create_buttons();
  for (const auto& b : buttons) {
    b.on_click();
  }
  buttons.front().on_click(); // counter has been incremented
  // Output "Beep: 0! Bop. Beep: 1!"
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