Lambdas in C++

So you wanna use lambdas in C++ huh? It's as simple as that:

auto lambda = []() = {
    printf("Hello, I am a simplest lambda.");
};

Now, if you wanna invoke it only once you can omit assigning value and either add parentheses at the end or use std::invoke():

[]() = {
    printf("Hello, I am a simplest lambda.");
}();

std::invoke([]() {
    printf("Hello, I am a simplest lambda.");
});

Or if you got a value you can just call it like any other function:

lambda(); 

What about parameters, return value? Just put them where they belong:

auto lambda = [](int a, int b) {
    return a + b;
};

int result = lambda(1, 2);

Guess we are done here, let's move on and talk about captures. Ok, see those square brackets over there? That's called Capture List, a place where you put your captures. A capture is an identifier of a variable defined outside your lambda and a method to copy(capture) it.

[] - empty brackets mean there is nothing to capture.
[count] - identifier means capturing a variable by value.

int count = 9;

auto lambda = [count]() {
    std::cout << count << std::endl;
};

[&count] - identifier with ampersand means capturing a variable by reference.

auto lambda = [&count]() {
    std::cout << count << std::endl;
};

[=] - means capturing all local variables used inside lambda by value.

void function()
{
int count = 9;

auto lambda = [=]() {
std::cout << count << std::endl;
};

lambda();
}

[&] - means capturing all local variables used inside lambda by reference.

void function()
{
int count = 9;

auto lambda = [&]() {
std::cout << count << std::endl;
};

lambda();
}

[this] - means capturing this pointer.

class ClassWithLambda
{
private:
  int count;

public:
  ClassWithLambda():count(9) {}

    void methodWithLambda()
    {
        auto lambda = [this]() {
std::cout << count << std::endl;
};

lambda();
}
};

Actually [=] and [&] capture this pointer too, if it exists:

class ClassWithLambda
{
private:
  int count;

public:
  ClassWithLambda():count(9) {}

  void methodWithLambda()
    {
  auto lambda = [=]() {
std::cout << count << std::endl;
};

lambda();
}
};

class ClassWithLambda
{
private:
  int count;

public:
  ClassWithLambda():count(9) {}

  void methodWithLambda()
    {
auto lambda = [&]() {
std::cout << count << std::endl;
};

lambda();
}
};