Re: modules, require, magic

[Philipp Janda <siffiejoe@...>]

On 21.10.2011 20:49, Sam Roberts wrote:
>
> [...]
> I'd say the single biggest problem with losing module is that we have
> to port everything to 5.2, and do it in a way that also works for 5.1
> (which will be here a long time).

Just use the proposed module-less module system -- it will work for Lua 
5.1 and 5.2 (no matter what is decided for the future of "module")!

> [...]
>
> For the common idiom of constructing
> modules in 5.2 to immediately require advanced metatable knowledge,
> seems unfortunate to me.
>
>    local _ENV = setmetatable({}, {__index=_G})
>    function foo() end
>    return _ENV

The proposed common idiom for 5.2 is:
local M = {}
function M.f() end
return M

No metatable or environment knowledge required at all for completely 
understanding what is happening!

> > 1. It handles constructing module tables including the fields _NAME, _M, and _PACKAGE. This is useful if one cares about these fields, but I note that they don't appear in the pre-defined modules like table and string.
>
> I use this in constructing modules from multiple files:
>
>    zbee/
>       init.lua -- this will require(_NAME..".app"), etc.

                 -- that would be require( (...)..".app"), now.

>       app.lua
>       link.lua
> [...]
> > 2. It handles constructing submodules. I might question whether it makes sense to have socket.http available when socket is potentially just a stub table, but that's a more complicated matter.
>
> I find hierarchical namespacing useful. I like that we can have
> fw/pump/tcp.lua, and that  tcp is not the same as
> protocol.tcp.lua. And doing
>
>    local fwpumptcp = require"fw.pump.tcp"
>    local protocoltcp = require"protocol.tcp"
>
> strikes me as awkward and silly.

You could also write:
local protocol = { tcp = require"protocol.tcp" }

The point is: The user of the module has the choice!

> [...]
>
> Our code doesn't use the global debug, but we do require our own
> frameworks, and we want them globally available, so testcase plugins
> can
>
>    require"tcp.plugin"
>
> and everything they might want is there. I don't want to start our
> plugins with 18 lines of
>
>    local blah = require"some.blah"
>
> statements.

$ cat > allmymodules.lua
return {
  tcp = require( "tcp.plugin" ),
  udp = require( "udp.plugin" ),
  raw = require( "raw.plugin" ),
  test = require( "test" ),
  other = require( "my.other.module" ),
  -- ...
}
^D

... which reduces your 18 lines to one line as it is now.

> [...]
>
> Cheers,
> Sam

Philipp