The question is from the torch5 tutorial: http://torch5.sourceforge.net/manual/torch/index-8-1.html
require "torch" -- for naming convenience do --- creates a class "Foo" local Foo = torch.class('Foo') --- the initializer function Foo:__init() self.contents = "this is some text" end --- a method function Foo:print() print(self.contents) end --- another one function Foo:bip() print('bip') end end --- now create an instance of Foo foo = Foo() --- try it out foo:print() --- create a class torch.Bar which --- inherits from Foo do local Bar = torch.class('torch.Bar', 'Foo') --- the initializer function Bar:__init(stuff) --- call the parent initializer on ourself self.__parent.__init(self) --- do some stuff self.stuff = stuff end --- a new method function Bar:boing() print('boing!') end --- override parent's method function Bar:print() print(self.contents) print(self.stuff) end end --- create a new instance and use it bar = torch.Bar("ha ha!") bar:print() -- overrided method bar:boing() -- child method bar:bip() -- parent's method After running this script, I got the error message:
/Users/frankhe/torch/install/bin/luajit: test1.lua:39: attempt to index field '__parent' (a nil value) Here is the picture of details: 
I want to know why this error happened.