How to design custom STL function objects to improve code reusability?

Using STL function objects can improve reusability, including the following steps: Define the function object interface (create a class and inherit from std::unary_function or std::binary_function) Overload operator() to define the function behavior in the overloaded Implement the required functions in operator() and use function objects through STL algorithms (such as std::transform)

Use STL function objects to improve code reusability

STL function object is a callable class that allows combining functional programming with object-oriented programming. By encapsulating code logic in function objects, you can improve reusability and encapsulation.

Steps:

1. Define the function object interface: Create a class that inherits from std::unary_function Or std::binary_function. Overload operator() to define function behavior.
2. Implement function logic: In the overloaded operator(), implement the required functions.
3. Using Function Objects: Function objects can be applied using STL algorithms like std::transform or std::for_each.

Example:

Suppose we want to create a function object to calculate the length of a string:

class StringLength {
public:
    int operator()(const std::string& str) {
        return str.length();
    }
};

int main() {
    std::vector<std::string> names = { "John", "Mary", "Bob" };

    std::vector<int> lengths;
    std::transform(names.begin(), names.end(), std::back_inserter(lengths), StringLength());

    for (int length : lengths) {
        std::cout << length << " ";  // 输出：4 4 3
    }
    std::cout << "\n";

    return 0;
}

In this example, StringLength The class is a function object that implements the logic of calculating the length of a string. We apply it to the string vector names via std::transform, storing the calculated length into the lengths vector.

By using custom function objects, we can achieve code reuse and easily apply the logic of calculating string length to different string collections.

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