Instantiating Lua objects through the C API - c++

Question

I am trying to do some OO functionality in Lua via the C API. In my Lua script I have the following:
Parser = {}
Parser.__index = Parser
function Parser:create(url)
local self = {}
print ("creating")
self.baseUrl = url
setmetatable(self, Parser)
return self
end
function Parser:Foo()
print ("baseUrl: " .. self.baseUrl)
end
p = Parser:create("http://www.google.com")
p:Foo()
If I run this from the command line, it works fine and I see the following output:
creating
baseUrl: http://www.google.com
Now, if I comment out the last two lines and try the following through the C API
// <load the state and lua file>
lua_getglobal(L, "Parser");
lua_getfield(L, -1, "create");
lua_pushstring(L, "http://www.google.com");
if (lua_pcall(L, 1, 1, 0) != 0)
{
// handle error
}
This works. I see "creating" in my standard output as expected. As I understand it, the new Parser object is now on top of the stack. If I them immediately try the following:
lua_getfield(L, -1, "Foo");
if (lua_pcall(L, 0, 0, 0) != 0)
{
logger()->error("-- %1", lua_tostring(L, -1));
}
I get the following error: attempt to index local 'self' (a nil value)
Can anyone tell me what I'm doing wrong and how to get the function to run as expected?
Thank you!

Answer 1

The definition function Parser:Foo() ... end is equivalent to:
Parser.Foo = function(self)
print ("baseUrl: " .. self.baseUrl)
end
That is -- Foo is a function that takes one argument. When you call lua_pcall(L, 0, 0, 0) you are passing 0 arguments. Change it to lua_pcall(L, 1, 0, 0) and everything should work. (You will have to also change the pcall to create to correctly pass 2 arguments rather than 1).