Writing a recursive lambda

Lambdas are basically unnamed function objects, which means that it should be possible to call them recursively. Indeed, they can be called recursively; however, the mechanism for doing so is not obvious as it requires assigning the lambda to a function wrapper and capturing the wrapper by reference. Though it can be argued that a recursive lambda does not really make sense and that a function is probably a better design choice, in this recipe, we will look at how to write a recursive lambda.

Getting ready

To demonstrate how to write a recursive lambda, we will consider the well-known example of the Fibonacci function. This is usually implemented recursively in C++, as follows:

constexpr int fib(int const n)
{
  return n <= 2 ? 1 : fib(n - 1) + fib(n - 2);
}

Having this implementation as a starting point, let’s see how we can rewrite it using a recursive lambda.

How to do it...

In C++11, in order to write a recursive lambda...