Example of a hostile Seeing is Believing environment

example_of_hostile_sib_environment.rb

# Users can fork the process, SiB still works
if !fork
  Process.pid # => 6669
else
  Process.pid # => 6668

  # Users can exec, SiB still works
  exec "echo users can exec, SiB still works" # printing is displayed at eof
end

# Close the input / output streams, SiB still works
[$stdin, $stdout, $stderr].each(&:close)

# Remove the `new` method, SiB still works
Class.class_eval { undef new }
String.new rescue $! # => #<NoMethodError: undefined method `new' for String:Class>
Array.new  rescue $! # => #<NoMethodError: undefined method `new' for Array:Class>

# Remove all the constants!, SiB still works
Object.class_eval do
  constants.each { |const| remove_const const rescue nil }
end
String rescue $! # => #<NameError: uninitialized constant String>
Object rescue $! # => #<NameError: uninitialized constant Object>

# remove all the methods from integers and strings, SiB still works
public def remove_all_methods
  instance_methods.each { |name| undef_method name }
end
1 + 1 # => 2
1.class.remove_all_methods
1 + 1 rescue $! # => #<NoMethodError: undefined method `+' for #<Integer:0x0000000000000003>>

# Okay, actually, removing all the string methods did actually crash the program >.<
# Anyway, here's that output from the exec back at the beginning:

# >> users can exec, SiB still works