NameError
Methods
M
Instance Public methods
missing_name()

Extract the name of the missing constant from the exception message.

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

Source: show | on GitHub 

# File activesupport/lib/active_support/core_ext/name_error.rb, line 10
def missing_name
  if /undefined local variable or method/ !~ message
    $1 if /((::)?([A-Z]\w*)(::[A-Z]\w*)*)$/ =~ message
  end
end
missing_name?(name)

Was this exception raised because the given name was missing?

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

Source: show | on GitHub 

# File activesupport/lib/active_support/core_ext/name_error.rb, line 24
def missing_name?(name)
  if name.is_a? Symbol
    self.name == name
  else
    missing_name == name.to_s
  end
end