gistfile1.rb

# Redefines const value during block execution.
#
# Usage example:
#   SOMECONST = 1     # SOMECONST == 1
#   redefine_const(:SOMECONST, 'hello') do
#     puts SOMECONST  # SOMECONST == 'hello'
#   end
#                     # SOMECONST == 1
def redefine_const(const, value, &block)
  if const_defined = Object.const_defined?(const)
    old_value = Object.const_get(const)
    Object.send(:remove_const, const)
  end
  Object.const_set(const, value)
  yield
ensure
  Object.send(:remove_const, const)
  Object.const_set(const, old_value) if const_defined
end