Table creation on demand for host application integration.

["Greg McCreath" <Greg.McCreath@...>]

Hi all,

I'm looking to find an elegant way around the lua:

a = {}

a.b.c = "x";

where 'b' must exist before 'c' can be assigned.  I wanted to create 'b'
on the fly.  Something like:

a = {};
mt = {};
setmetatable(a, mt)

mt.__newindex = function (table, key)
  return {};
end

a.b.c = 10;  -- this should create 'b'
print(a.b.c)


... which, of course, blows up.  But I want 'b' to be created and
assigned to 'a' when it is asked for.

Why?  Well 'a' represents an external list of structures in the host
application.  Let's call them 'products'.  I'd like to represent these
products and their attributes to lua script as a table.  Nice and
elegant.  Such that I can do:

a.product100.qty = 10;

so that when the 'product100' key is not found a table can be supplied
with meta methods that can manipulate the external host-application
fields of that given product.

Some of the attributes of products are themselves structures.  Expand
this example to:

a.product100.barcode.type = "EAN13"

and so on.  None of my crazy experiments have managed to get this to
work ...

Many thanks, all help appreciated.

Greg.




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