Functional programming techniques in C++

There are many excellent programming techniques in the C language, among which functional programming is a very practical technology. Functional programming emphasizes the reusability and flexibility of functions, which can make the code clearer and maintainable. In this article, we will introduce functional programming techniques in C.

1. Function object

The function object is a callable object, which can be regarded as a function. Function objects in C can be class objects or function pointers. Function objects can be used in STL algorithms and can also be used as parameters of other functions. The following is a simple example of a function object:

class Add
{
public:
    int operator()(int x, int y) const
    {
        return x + y;
    }
};

int main()
{
    Add add;
    int result = add(1, 2);
    return 0;
}

The Add class in this example overloads the () operator, so the Add object can be called like a function. Using function objects can make your code more concise and flexible.

2. Lambda expression

Lambda expression is a new language feature introduced in C 11, which can easily define anonymous functions. The basic syntax of lambda expression is:

[capture list] (parameter list) -> return type { function body }

Among them, capture list is the list of variables that the lambda expression needs to capture; parameter list is the parameter list of the lambda expression; return type is the value of the lambda expression. Return value type; function body is the function body of the lambda expression.

The following is a simple lambda expression example:

auto add = [] (int x, int y) -> int { return x + y; };
int result = add(1, 2);

The lambda expression in this example defines an add function, which accepts two int type parameters and returns their sum.

3. std::function

std::function is a function object template class in C 11, which can store any callable object. Using std::function can conveniently pass function objects and lambda expressions, and can also be used to implement callback functions and other scenarios. The following is a simple std::function example:

std::function<int(int, int)> add = [] (int x, int y) -> int { return x + y; };
int result = add(1, 2);

In this example, a std::function object add is defined, which can accept two int type parameters and return their sum. Assigning lambda expressions to std::function objects enables the storage and transfer of function objects.

4. Currying

Currying is a technique that converts a function with multiple parameters into a sequence of functions that accepts a single parameter. Currying can make functions more flexible and can be used to implement functions such as partial application functions. To implement currying in C, you can use function objects and lambda expressions.

The following is an example of currying of a function object:

class Add
{
public:
    int operator()(int x) const
    {
        return x + y;
    }

private:
    int y;
};

int main()
{
    Add add;
    add(1)(2); // 返回3
    return 0;
}

The Add class in this example implements currying. It can accept a parameter x and then return one to accept another parameter. The function object of y. The calculation of multi-parameter functions can be achieved through continuous calls.

The following is an example of currying a lambda expression:

auto add = [] (int x) {
    return [=] (int y) {
        return x + y;
    };
};

int main()
{
    int result = add(1)(2); // 返回3
    return 0;
}

The lambda expression in this example returns a function object that accepts a parameter y and then returns x and y of and. Currying can be achieved through lambda expressions.

Summary

This article introduces functional programming techniques in C, including function objects, lambda expressions, std::function, and currying. These techniques can make the code more flexible and readable, and can improve the maintainability and reusability of the code. In actual program development, reasonable application of these techniques can improve the quality and efficiency of the code.

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