As a software developer C++ 11 when should I use the keyword noexcept in lambda function?

As a software developer, you should use the noexcept keyword in lambda functions when you know that the lambda does not throw any exceptions, in order to help the compiler optimize the code.

lambda simple usage

For example, if you have a lambda that performs a simple mathematical operation or a call to a non-throwing function, you can use noexcept to indicate that the lambda does not throw:

auto lambda = []() noexcept { return 5 + 7; };

Another one.

auto lambda = []() noexcept { std::cout << "Hello World" << std::endl; };

lambda with containers

If you are using a lambda as a comparator for a container that requires noexcept move constructors.

std::vector<int> v = {3, 1, 4, 1, 5, 9};
std::sort(v.begin(), v.end(), [](const auto& a, const auto& b) noexcept { return a < b; });

For example, suppose you have a std::vector<std::function<void()>> and you want to add a lambda to it. If the lambda does not throw any exceptions, you can use the noexcept keyword to indicate this to the compiler and make the vector's move operations more efficient:

std::vector<std::function<void()>> v;
v.push_back([]() noexcept { /* code that does not throw */ });

lambda in functor

Another example is when you are creating a custom functor that is intended to be used in a noexcept context, you can use the noexcept keyword to indicate that this functor is not going to throw:

class MyFunctor {
public:
    void operator()() const noexcept { /* code that does not throw */ }
};

lambda as a callback function

Additionally, when you are passing a lambda as a callback function, and the function that takes the callback expects it to be noexcept, you should use the noexcept keyword to indicate this.

void set_callback(std::function<void() noexcept> callback) { /* ... */ }
set_callback([]() noexcept { /* ... */ });

It is important to note that marking a function as noexcept is not a guarantee that it will never throw an exception. If a noexcept function throws an exception, the program will terminate. Therefore, it is important to ensure that your noexcept functions do not throw, and to use the noexcept keyword only when you are sure that the function does not throw.

As a software developer C++ 11 when should I use the keyword noexcept in lambda function?