Re: [proposal / postulation]: global keyword that works with lua as config file

[David Favro <lua@...>]

On 03/30/2014 01:57 PM, Andrew Starks wrote:

> `strict` is available and works well.
I'm not sure I agree that it works well: it is problematic in that it 
doesn't support name scoping, by which I mean this will raise an error:
require("strict");
local foo = require("foo"); --< a global is set in the module definition

As a user of module "foo", I have no way of knowing if it pollutes the 
global namespace or not, and I've found that some popular ones do.  If I 
require() all of my needed modules prior to require()ing "strict", I am 
still not safe:

local foo = require("foo");
require("strict");
local bar = foo.bar(); --< global is set in this function

Again, as a user of module "foo", I have no way of know if and when it will 
set a global, and once I require("strict") no module is usable that doesn't 
promise to never set a global as part of its "contract".

It might be possible to try to load modules using their own private 
environments, which aren't strict-protected, but aside from being a PITA 
[require() has no environment parameter, I guess loadfile() would be 
needed], I suspect that this will introduce a lot of other problems.

The same problem arises when creating modules, only inverted: if I 
require("strict") from within my module-definition (unless I take special 
precautions to put my module into its own environment), I am likely to break 
any code which require()s my module, if it ever sets a global -- so it's 
effectively verboten to do so from anywhere within a module, and (static 
analysis tools aside) it's difficult to detect subtle bugs in my module due 
to a forgotten 'local'.

So, I suggest that any proposed innate strict-global feature should have 
some mechanism to (perhaps optionally) only be enforced for accesses to the 
global environment from the chunk in which it is specified; _STRICT as 
proposed does not respect this.  Thinking along these lines, what I think 
might be more useful than throwing runtime errors, and perhaps even easier 
to implement, is a mechanism to specify default-local rather than 
default-global for names declared _just_ within a particular chunk.  Either 
or both would be welcome.

-- David