
#define CATCH_CONFIG_MAIN
#include <catch2/catch.hpp>


#include <vector>
#include <string>
#include <algorithm>
#include <functional>

struct Student {
    std::string name;
    int grade;
};

std::function<bool(const Student&, const Student&)> my_lambda();

TEST_CASE("Lambda comparator sorts students by grade descending", "[my_lambda]") {
    std::vector<Student> students = {
        {"Alice", 85},
        {"Bob", 92},
        {"Charlie", 78},
        {"Diana", 90}
    };
    std::sort(students.begin(), students.end(), my_lambda());
    REQUIRE(students[0].name == "Bob");
    REQUIRE(students[0].grade == 92);
    REQUIRE(students[1].name == "Diana");
    REQUIRE(students[1].grade == 90);
    REQUIRE(students[2].name == "Alice");
    REQUIRE(students[2].grade == 85);
    REQUIRE(students[3].name == "Charlie");
    REQUIRE(students[3].grade == 78);
}

TEST_CASE("Lambda comparator works with equal grades", "[my_lambda]") {
    std::vector<Student> students = {
        {"Eve", 80},
        {"Frank", 80},
        {"Grace", 95}
    };
    std::sort(students.begin(), students.end(), my_lambda());
    REQUIRE(students[0].name == "Grace");
    REQUIRE(students[0].grade == 95);
    REQUIRE(students[1].grade == 80);
    REQUIRE(students[2].grade == 80);
}

TEST_CASE("Lambda comparator handles empty vector", "[my_lambda]") {
    std::vector<Student> students;
    std::sort(students.begin(), students.end(), my_lambda());
    REQUIRE(students.empty());
}

TEST_CASE("Lambda comparator handles single element", "[my_lambda]") {
    std::vector<Student> students = { {"Henry", 88} };
    std::sort(students.begin(), students.end(), my_lambda());
    REQUIRE(students.size() == 1);
    REQUIRE(students[0].name == "Henry");
    REQUIRE(students[0].grade == 88);
}

test.cpp

Master the power of modern C++ lambdas — from writing concise inline functions to capturing variables efficiently. Explore how lambdas simplify code structure, enable functional programming patterns, and enhance flexibility when used with STL algorithms. Learn to handle captures, mutable states, and return types with precision. By the end, you’ll be able to use lambdas confidently for cleaner, faster, and more expressive C++ code.

Discover what lambda expressions are, why they were introduced, and how to use their basic syntax and variable capturing.

Explore more sophisticated lambda capabilities, including capture modes, mutability, and explicit return types.

See how lambdas unlock powerful patterns in the C++ Standard Library, especially with algorithms.

Challenge: Sort Structs with a Lambda

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