Lambda Expressions

Code

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

int main() {
    int x = 10, y = 20;

    // Capture by value
    auto add1 = [x, y]() { return x + y; };

    // Capture by reference
    auto add2 = [&x, &y]() { return x + y; };

    // Capture all by value
    auto add3 = [=]() { return x + y; };

    // Capture all by reference
    auto add4 = [&]() { x++; y++; };

    // Mixed capture
    auto mixed = [x, &y]() { y += x; };

    // mutable Lambda
    int count = 0;
    auto counter = [count]() mutable { return ++count; };

    // Generic Lambda (C++14)
    auto print = [](const auto& v) {
        std::cout << v << std::endl;
    };
    print(42);
    print("hello");

    // Used in STL algorithms
    std::vector<int> nums = {3, 1, 4, 1, 5, 9};
    std::sort(nums.begin(), nums.end(), [](int a, int b) {
        return a > b; // Descending order
    });

    // std::function storage
    std::function<int(int, int)> op = [](int a, int b) { return a * b; };
    std::cout << op(3, 4) << std::endl;

    return 0;
}

Explanation

Lambda captures variables via the [] capture list; = captures by value, & by reference; mutable allows modifying captured values.

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