Re: Binding modules loaded by "require"?

On 12/17/2009 5:22 AM, Kristoffer Danielsson wrote:
> Thanks for your reply.
>
> I've read the documentation, but I don't quite follow.
>
> If I load "C:\MyScript.lua" and do my luabind stuff:
>
> luabind::open(L);
> bind "foo" etc...
>
> And then, inside this MyScript.lua, I want to get access to another 
> library:
>
> require 'extra.mylib' -- Loads C:\extra\mylib.lua...
>
> Now, inside mylib.lua I want to access my C++ function "foo". You 
> mention "preload", but where should I initialize it - and how?
>
> Thanks again!

The documentation under "require" tells you exactly why 
"require 'extra.mylib'" causes "C:\extra\mylib.lua" to be loaded. This 
happens exactly and only because there is an entry in the 
"package.loaders" array that tells it to convert "extra.mylib" into a 
Lua filename "\extra\mylib.lua". The package system, when you 
initialized it, causes this to happen.

Specifically, the documentation under "package.loaders" explains how it 
works:

Each entry in this table is a /searcher function/. When looking for a 
module, |require| 
<http://www.lua.org/manual/5.1/manual.html#pdf-require> calls each of 
these searchers in ascending order, with the module name (the argument 
given to |require| 
<http://www.lua.org/manual/5.1/manual.html#pdf-require>) as its sole 
parameter. The function can return another function (the module 
/loader/) or a string explaining why it did not find that module (or 
*nil* if it has nothing to say). Lua initializes this table with four 
functions.

Therefore, all "require" does is call functions in "package.loaders". 
So, if you want to provide a hook into the package system to be able to 
create your own C/C++ packages, you simply modify this array. Add a 
C/C++ function into the array that takes a string. This function will be 
called when a user uses "require", as long as none of the earlier loaders.

The initial form of "package.loaders" looks like this:

package.loaders[1] = function(moduleName) if(package.preload[moduleName] 
&& type(package.preload[moduleName]) == "function") then return 
package.preload[moduleName] else return nil end end
package.loaders[2] = function(moduleName) --[[ Search package.path for a 
Lua file with moduleName. ]] end
package.loaders[3] = function(moduleName) --[[ Search package.cpath for 
a DLL/SO file with moduleName. ]] end
package.loaders[4] = function(moduleName) --[[ Search package.cpath for 
a DLL/SO file with moduleName's root name. ]] end

You can add/change one of these functions, or you can simply add an 
entry in "package.preload[moduleName]" for your module's name.

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