Re: modifying a module with another module

["Jerome Vuarand" <jerome.vuarand@...>]

2008/9/23 Wesley Smith <wesley.hoke@gmail.com>:
> Hi List,
> Here's a fairly simple idea that seems fraught with gotchas.  I have a
> GUI module that binds some C++ classes and presents them as a Lua
> module.  It's quite spare and I want to keep it that way.  I've
> designed the bindings to allow for heavy augmentation within Lua
> scripts and I now want to design a module that codifies some of these
> augmentations.  To make things concrete, here's the module layout:
>
>
> require 'glv' -- widget library (contains a View widget)
>
> I now want to make a 'glvutils' module that augments glv.View by
> extending one of it's methods.  If I call View:add(widget) the widget
> will become a child of View.  I'd like to have the function View:add
> perform additional tasks.  Currently, I'm doing:
>
> ------------------------------- glvutils module code:
>
> local glv = require "glv"
> local View = glv.View
>
> -- initializer functions that programmatically modify the glv module
> local
> function nameadd(f)
>        return
>        function(self, v)
>                local name = v.name
>                if(name) then
>                        print("nameadd", name)
>                        local children = self.children or {}
>                        children[name] = v
>                        self.children = children
>                end
>                f(self, v)
>        end
> end
>
> local
> function adapt_glv(m)
>        -- widgets to modify
>        local parent_widgets = {
>                View = View,
>        }
>
>        for name, w in pairs(parent_widgets) do
>                -- add new functionality to widget:add function
>                w.add = nameadd(w.add)
>
>                -- put the modified widgets in the module table
>                m[name] = w
>        end
> end
>
> module('glvutils', adapt_glv)
> --------------------------------------------------------------------
>
> An issue I have with the above is that if I require "glv" _after_ I
> require "glvutils", the View:add function will be the one created by
> the glvutils module, not the original glv module one.  Is there a way
> around this?  Do I have to duplicate the table?  This could pose some
> problems if View itself has a metatable or an environment.  Thanks for
> any ideas about this.

Can you explain what View is ? Is that a singleton ? A prototype ? A
class ? If so how did you implement your class system ? Are your
objects userdata, tables ? How are their methods defined and where are
they located ?