How to delete class variable in Torch?

Question

I have problems in understanding how a class variable in Torch works.

I did the following:

mydata=torch.class('something')

I checked the User variable by typing who() and it shows:

== User Variables ==
[_RESULT]        = table - size: 0
[mydata]         = table - size: 0
[something]      = table - size: 0

I first of all tried to delete mydata by

mydata=nil 

it works. mydata is now freed and can be reinitialized to any values. But when I tried to delete the variable something by typing

soemthing=nil

It seems it's not working even though the variable something was not list in who() anymore. When I try:

mydata2=torch.class('something')

the error pops out:

/data/torch/install/share/lua/5.1/torch/init.lua:65: something has been already assigned a factory
stack traceback:
        [C]: in function 'newmetatable'
        /data/torch/install/share/lua/5.1/torch/init.lua:65: in function 'class'
        [string "mydata2=torch.class('something')"]:1: in main chunk
        [C]: in function 'xpcall'
        /data/torch/install/share/lua/5.1/trepl/init.lua:648: in function 'repl'
        /data/torch/install/lib/luarocks/rocks/trepl/scm-1/bin/th:185: in main chunk
        [C]: at 0x00406670

Could anyone tell me the reason behind it?

Answer 1

torch.class() stores the class metatable in the lua-registry, see http://www.lua.org/pil/27.3.1.html and the luaT_lua_newmetatable() function in the torch C-backend.

In order to unregister an existing class it is necessary to remove the entry from the lua-registry. You can access the registry from lua with help of the debug.getregistry() function.

With removeal from registry your example works:

mydata = torch.class('something')
mydata = nil
soemthing = nil

-- remove the global registration:
debug.getregistry()['something'] = nil    

-- now it is possible to register the class again
mydata2 = torch.class('something')