Strange interaction with nn.Container

[davidBelanger]

Below is a minimal piece of code demonstrating a strange bug I have experienced.

Here, I have a typical LSTM sequence encoder. I also have a dummy class that inherits from nn.Container. The following code crashes. However, if you move the
parent:__init(self) line to go after mapper:forward(), then everything is ok. It fails in dpnn.Module:

   if moduleClones then
      assert(self.modules == nil)
      self.modules = modules
      clone.modules = moduleClones
   end

Since the container has a member called modules, this code crashes. It seems like the self pointer is wrong here or something. Any ideas about what is going on?

require 'nn'
require 'rnn'

local vocabSize = 25
local embeddingDim = 10
local rnnHidSize = 15

local lstm = nn.Sequencer(nn.LSTM(embeddingDim, rnnHidSize))
local mapper = nn.Sequential():add(nn.LookupTable(vocabSize,embeddingDim)):add(nn.SplitTable(2)):add(lstm):add(nn.SelectTable(-1))

--this is a minibatch of 'sentences'
local data = torch.rand(32,16):mul(vocabSize):ceil()


local NoopContainer, parent = torch.class('nn.NoopContainer', 'nn.Container')

function NoopContainer:__init()
    parent:__init(self)

    local length = 12
    local dd = torch.rand(32,length):mul(vocabSize):ceil()
    mapper:forward(dd)

end


local noop = nn.NoopContainer()

[nicholas-leonard]

@davidBelanger Wow this is some weird stuff. Looking into it.

[nicholas-leonard]

@davidBelanger Found the problem :

parent:__init(self)

should be replaced with

parent.__init(self)

Effectively, self was the Module class, thereby setting the modules attribute for all Module subclasses :)

[davidBelanger]

Awesome! Thank you very much for the help. This fixed it.