Re: local "module" pattern without module [was Re: [ANN] SLAXML - pure Lua, robust-ish, SAX-like streaming XML processor]

[Bernd Eggink <monoped@...>]

On 18.02.2013 18:46, Gavin Kistner wrote:
> Put more simply: how would you rewrite the following suite of files so
> that the user can "require 'master'" and not spam the global namespace
> with "MASTER", but still have all the assertions pass?
>
>      ### _test_usage_.lua
>      require 'master'
>      assert(MASTER.Simple)
>      assert(MASTER.simple)
>      assert(MASTER.Shared)
>      assert(MASTER.Shared.go)
>      assert(MASTER.Simple.ref1()==MASTER.Multi1)
>      assert(pcall(MASTER.Simple.ref2))
>      ### master.lua
>      MASTER = {}
>      require 'simple'
>      require 'multi'
>      require 'shared1'
>      require 'shared2'
>      require 'reference'
>      ### simple.lua
>      MASTER.Simple = {}
>      function MASTER:simple() end
>      ### multi.lua
>      MASTER.Multi1 = {}
>      MASTER.Multi2 = {}
>      ### shared1.lua
>      MASTER.Shared = {}
>      ### shared2.lua
>      function MASTER.Shared:go() end
>      ### reference.lua
>      function MASTER.Simple:ref1() return MASTER.Multi1 end
>      function MASTER.Simple:ref2() MASTER:simple()      end

I use an "auto-require" mechanism for that. My master module contains a 
table which maps each public function or variable to a source file. The 
module table itself has a metatable with a __index function which looks 
up the name and then automatically calls require(file). Apart from its 
metatable, the master module is an empty table.
After setting this up, any submodule and any application only has to 
require the master module explicitly. The rest is done automatically.

Here is skeleton of the master module:

------------------------------------------------
local M = {}
package.loaded[...] = M
local submodules = {
	foo = 'file1.lua',
	bar = 'file1.lua',
	baz = 'file2.lua',
	...
}
setmetatable(M, { __index = function(tbl, key)
    local v = rawget(submodules, key)
    if v then
        require(v)
        return rawget(M, key)
    end
    error(key .. ' not found!')
end })
return M
------------------------------------------------

Of course this mechanism relies on the completeness of the 'submodules' 
table. But I found that if you follow a certain coding discipline, the 
complete master module can easily be created by a little Lua program.

Hope that helps.
Regards, Bernd
--
http://sudrala.de