[Lua 5.2] Object Oriented Programming with _ENV

[Patrick Donnelly <batrick@...>]

(Forgive me if someone has noted this before; I don't recall any
discussion on it.) It recently occurred to me that you can use _ENV to
setup methods that look like popular object oriented languages (such
as Java). For example:

function Class:Method (bar)
  local _ENV = self;
  foo = bar -- assign self.foo = bar
end

This isn't easily doable in Lua 5.1 because environments are set on
the function itself (and would change the method for all objects)
whereas in the above case this only changes the method environment for
the given execution frame.

You can also automate this process by doing:

function Class.Method (_ENV, bar, x)
  foo = bar -- assign self.foo = bar
  _ENV.x = x -- names collide, similar to this.x = x in Java
end

I thought this was a pretty neat side effect of the new environments
for Lua 5.2 and worth sharing. The _ENV name makes it confusing for
beginners since the name doesn't make a whole lot of sense. It also
complicates getting global functions like pairs.

-- 
- Patrick Donnelly