Apprendre Function Composition | Working with Predicates and Algorithms

Function composition is a powerful technique that lets you combine multiple functions or predicates to build more complex operations from simpler ones. In C++, you can achieve function composition and chaining by using lambdas and standard algorithms. This approach is especially useful when you want to apply a series of transformations or filters to collections, such as vectors, in a concise and expressive way. By composing functions, you can create pipelines where the output of one function becomes the input of the next, making your code modular and easier to maintain.

main.cpp


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#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> numbers{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

    // First lambda: filter even numbers
    auto is_even = [](int x) { return x % 2 == 0; };

    // Second lambda: square a number
    auto square = [](int x) { return x * x; };

    // Compose: filter then transform
    std::vector<int> evens;
    std::copy_if(numbers.begin(), numbers.end(), std::back_inserter(evens), is_even);

    std::vector<int> squared_evens;
    std::transform(evens.begin(), evens.end(), std::back_inserter(squared_evens), square);

    std::cout << "Squared even numbers: ";
    for (int n : squared_evens) {
        std::cout << n << " ";
    }
    std::cout << std::endl;

    return 0;
}

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Section 2. Chapitre 4

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main.cpp


              1234567891011121314151617181920212223242526272829
            
#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> numbers{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

    // First lambda: filter even numbers
    auto is_even = [](int x) { return x % 2 == 0; };

    // Second lambda: square a number
    auto square = [](int x) { return x * x; };

    // Compose: filter then transform
    std::vector<int> evens;
    std::copy_if(numbers.begin(), numbers.end(), std::back_inserter(evens), is_even);

    std::vector<int> squared_evens;
    std::transform(evens.begin(), evens.end(), std::back_inserter(squared_evens), square);

    std::cout << "Squared even numbers: ";
    for (int n : squared_evens) {
        std::cout << n << " ";
    }
    std::cout << std::endl;

    return 0;
}

Tout était clair ?

Merci pour vos commentaires !

Section 2. Chapitre 4