Lambdas

# Creating Recursive Lambdas

## Can a lambda call itself recursively?

Yes, a lambda can call itself recursively. However, because lambdas don't have a name by default, you need to use a special technique to achieveÂ this.

The trick is to capture a reference to the lambda itself using a std::function. Here's an example that calculates the factorial of a number using a recursiveÂ lambda:

#include <iostream>
#include <functional>

int main() {
std::function<int(int)> factorial{
[&factorial](int n) {
if (n <= 1) {
return 1;
} else {
return n * factorial(n - 1);
}
}
};

std::cout << "Factorial of 5: "
<< factorial(5) << '\n';
}
Factorial of 5: 120

Here's how thisÂ works:

1. We declare aÂ std::functionÂ namedÂ factorial. This will hold our lambda.
2. We initializeÂ factorialÂ with a lambda that takes an integerÂ nÂ and returns an integer.
3. Inside the lambda, we check the base case (n <= 1). If this is true, we return 1.
4. If the base case is not met, we returnÂ n * factorial(n - 1). This is where the recursion happens.
5. Importantly,Â factorialÂ is captured by reference in the lambda. This allows the lambda to call itself through theÂ factorialÂ variable.

When we call factorial(5), it will recursively compute the factorial of 5, which isÂ 120.

This pattern can be used to create recursive lambdas for various tasks. However, it's important to ensure that your recursive lambda has a base case that stops the recursion, otherwise you'll get infinite recursion and a stackÂ overflow.

Also note that recursive lambdas can be less efficient than iterative solutions due to the overhead of function calls. However, they can be useful in situations where a recursive solution is more clear andÂ concise.

Remember that this technique requires capturing the lambda by reference. Be careful not to let the reference outlive the lambda, as this will result in undefinedÂ behavior.

This Question is from the Lesson:

### Lambdas

An introduction to lambda expressions - a concise way of defining simple, ad-hoc functions

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This Question is from the Lesson:

### Lambdas

An introduction to lambda expressions - a concise way of defining simple, ad-hoc functions

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