class NameError

def missing_name

# => "HelloWorld"
end
e.missing_name
rescue NameError => e
HelloWorld
begin

Extract the name of the missing constant from the exception message. 
def missing_name
  # Since ruby v2.3.0 `did_you_mean` gem is loaded by default.
  # It extends NameError#message with spell corrections which are SLOW.
  # We should use original_message message instead.
  message = respond_to?(:original_message) ? original_message : self.message
  return unless message.start_with?("uninitialized constant ")
  receiver = begin
    self.receiver
  rescue ArgumentError
    nil
  end
  if receiver == Object
    name.to_s
  elsif receiver
    "#{real_mod_name(receiver)}::#{self.name}"
  else
    if match = message.match(/((::)?([A-Z]\w*)(::[A-Z]\w*)*)$/)
      match[1]
    end
  end
end

def missing_name?(name)

# => true
end
e.missing_name?("HelloWorld")
rescue NameError => e
HelloWorld
begin

Was this exception raised because the given name was missing? 
def missing_name?(name)
  if name.is_a? Symbol
    self.name == name
  else
    missing_name == name.to_s
  end
end

def real_mod_name(mod) 

def real_mod_name(mod)
  UNBOUND_METHOD_MODULE_NAME.bind_call(mod)
end