Re: Some ways to get encapsulation in Lua

[PA <petite.abeille@...>]

On Jan 25, 2005, at 19:49, Mark Hamburg wrote:

> Function closures
> -----------------
> This is covered in Programming in Lua. Since a function can reference
> upvalues and clients can't look inside without using the debug 
> interface --
> and in any context where encapsulation mattered, one should probably 
> remove
> the debug interface. The chief downside is that construction and usage 
> don't
> have much in common with other approaches to implementing objects in 
> Lua.

One thing that I like with this approach is that, beside providing 
encapsulation, it provides, er, "visual encapsulation". In other words, 
the entire object is defined inside one function. This is pretty neat 
:)

For example:

// Root class

function LUObject()
    local self = {}

    local description = function()
	    print "default description method"
    end

    return
    {
	    description = description
    }, self
end

// A subclass

function MySubclass()
    local self, super = LUObject();

    local description = function()
	    print "my very own description as well"
	    super.description()
    end

    return
    {
	    description = description
    }, self
end

And finally:

anObject = MySubclass()
anObject.description()

As an added deviance, if you wanted to make a class <gasp> "final" 
</gasp>, you would not return "self" at the end of an "object" 
function... scary thought :o)

Would the above scheme provide both inheritance and encapsulation 
without too much fuss?

Cheers

--
PA
http://alt.textdrive.com/