Recursive Functions

In this lesson you will learn how to write a recursive method in Ruby and understand the basic idea of a function that calls itself. This is for anyone searching for "Ruby recursive function how to use".

A recursive function is a function that calls itself. It suits work that repeats the same calculation pattern, such as "n! = n x (n-1)!". Always provide a stopping condition, or it will call itself forever and the program will crash.

The sample code has factorial keep calling itself as n * factorial(n - 1) until it reaches the stopping condition return 1 if n <= 1. The one-line stopping condition using a trailing if is compact, idiomatic Ruby.

A common stumbling block for beginners is forgetting that stopping condition and recursing forever. Deep recursion also consumes a lot of stack, so it is worth considering whether a loop would do instead.

In real-world development, recursion is a natural fit for hierarchical data such as folder trees or nested comment replies. Understand the mechanism once and you will find it applies widely.

📖 Reference code

def factorial(n)
  return 1 if n <= 1
  n * factorial(n - 1)
end
puts factorial(5)

✍️ Your code

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