Re: Require

[Mark Hamburg <mhamburg@...>]

Yes, export puts values in the dictionary used by import.

I thought about making import just use the __index metamethod but was left
feeling fuzzy on what to do in the event of an error. If it really acts just
like a table, then it should just return nil if the value isn't present.
True an __index metamethod can throw an exception, but that's a departure
from what the syntax would lead one to expect.

I like your implementation. It's a bit simpler than mine. On the other hand,
the complexity in mine may be from the fact that I take explicit steps to
detect and disallow cyclic import.

I've been thinking of extending my import function to allow specifying a
series of names to extract from the exported value:

    local _, addObserver, removeObserver, notifyObservers =
        import( "com.baymoon.Observations", "add", "remove", "notify" )

Missing names would trigger an exception at import time.

Mark

on 7/24/04 5:56 PM, Rici Lake at lua@ricilake.net wrote:

> That is very pretty.
> 
> I assume when you say "exports one or more named values" that you mean
> that it exports them to the dictionary import() uses? In that
> case, you could even make import the dictionary, instead of a
> function, and define an __index metamethod.
> 
> That would make the implementation something like this, leaving out
> the interesting parts (like the bundle-finder and the bundle-runner):
> 
> import = setmetatable({}, {__index =
>  function(self, name)
>    local bundle, bundlename = findBundleForName(name)
>    setfenv(bundle, setmetatable({}, {__index = getfenv(0)})
>    local exports = bundle()
>    for k, v in exports do
>      if rawget(self, k) == nil then self[k] = v end
>    end
>    local rv = rawget(self, name)
>    if rv == nil then
>      error(bundlename .. " did not export " .. name)
>    end
>    return rv
>  end})
> 
> -------
> 
> local showRect = import.showRect