Re: local "module" pattern without module [was Re: [ANN] SLAXML - pure Lua, robust-ish, SAX-like streaming XML processor]
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- Subject: Re: local "module" pattern without module [was Re: [ANN] SLAXML - pure Lua, robust-ish, SAX-like streaming XML processor]
- From: Bernd Eggink <monoped@...>
- Date: 2013年2月18日 20:40:13 +0100
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