How do I raise a fatal exception ruby?

Question

Ruby has a fatal exception, but there is no guidance on how to raise it and I cannot figure it out. How do I raise a fatal exception in Ruby?

Answer 1

Sure you can.

Try this

FatalError = ObjectSpace.each_object(Class).find { |klass| klass < Exception && klass.inspect == 'fatal' }

And then

raise FatalError.new("famous last words")

How does this work?

• fatal is an internal class without associated top-level constant
• ObjectSpace.each_object(Class) enumerates over all classes
• find { ... } finds an exception class named "fatal"

---

NB though, despite its name fatal is not special, it can be rescued. If you are looking for a way to end your program maybe best call the global exit method?

begin
  raise FatalError.new
rescue Exception => e
  puts "Not so fatal after all..."
end

Answer 2

Short answer is, you can, but probably shouldn't. This exception is reserved for Ruby internals. It is effectively hidden to users by being a constant with an all lowercase identifier. (Ruby won't do a constant lookup unless the identifier starts with an uppercase character.)

fatal
NameError: undefined local variable or method `fatal' for main:Object

The same is true when using Object#const_get:

Object.const_get(:fatal)
NameError: wrong constant name fatal

If this exception class was intended for us to use, then it would be readily available, and not hidden away.