EC
SystemStackError
RubyFATALCommonSystem

Stack overflow from infinite recursion

Quick Answer

Add a base case to recursive methods; convert deep recursion to iteration or use tail-call optimisation.

What this means

Raised when the call stack grows beyond its limit, almost always due to infinite or runaway recursion. It is a subclass of Exception. The default Ruby stack depth is typically around 10,000–15,000 frames.

Why it happens
  1. 1Recursive method with a missing or unreachable base case
  2. 2Circular method_missing delegation
  3. 3Accidental infinite loop that calls a method each iteration

Fix

Add an explicit base case

Add an explicit base case
def factorial(n)
  return 1 if n <= 1   # base case prevents infinite recursion
  n * factorial(n - 1)
end

Why this works

The base case terminates recursion when n reaches 1, unwinding the stack cleanly.

Code examples
Infinite recursionruby
def boom
  boom
end
boom
# SystemStackError: stack level too deep
Iterative alternativeruby
def sum_to(n)
  (1..n).reduce(0, :+)   # no recursion, no stack risk
end
Rescue (emergency only)ruby
begin
  deeply_nested_operation
rescue SystemStackError => e
  puts "Stack overflow: #{e.message}"
end
Sources
Official documentation ↗

Ruby Core Documentation

Content generated with AI assistance and reviewed for accuracy. Found an error? hello@errcodes.dev

← All Ruby errors