ruby_closure_exploration.rb

greeting = "Hello"

def dumb_greeter
  puts greeting
end

def invasive_greeter(b)
  puts b.eval("greeting")
end

block_greeter = ->{puts greeting}

def parent_greeter
  greeting = "Hello"
  child_greeter
end

def child_greeter
  puts greeting
end

dumb_greeter
# NameError: undefined local variable or method `greeting' for main:Object

invasive_greeter binding()
# Hello

block_greeter.call
# Hello

parent_greeter
# NameError: undefined local variable or method `greeting' for main:Object