gistfile1.rb

def takes_an_optional_block(&block)
  block_given_for_optional = block_given?
  stash_block {
    block_given_for_stash = block_given?
    puts "block_given_for_optional: #{block_given_for_optional}"
    puts "block_given_for_stash: #{block_given_for_stash}"
  }
end

def stash_block(&block)
  $block = block
end

def call_stashed
  puts "block_given for call_stashed: #{block_given?}"
  $block.call
end

takes_an_optional_block { "foo" }
call_stashed

puts "\nround 2:"
takes_an_optional_block
call_stashed

puts "\nround 3:"
takes_an_optional_block
call_stashed { "bar" }

gistfile2.txt

block_given for call_stashed: false
block_given_for_optional: true
block_given_for_stash: true

round 2:
block_given for call_stashed: false
block_given_for_optional: false
block_given_for_stash: false

round 3:
block_given for call_stashed: true
block_given_for_optional: false
block_given_for_stash: false