Re: Matter of class/instance form/function...

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

On Sep 16, 2007, at 09:01, Daniel Collins wrote:

> This is pretty much your option three. The advantage is that by using
> the prototype (or class table) as the metatable for class instances, 
> you
> don't require the additional table per instance. It also works well 
> with
> inheritance, as described in PiL.


FWIW, I pretty much given up on OO in Lua, but during my OO period I 
settled for PiL's approach as well:

http://www.lua.org/pil/16.1.html


The base class does something along these lines:

-- factory method
function self:new( ... )
        local anObject = {}
        local aClass = self:class()

        setmetatable( anObject, aClass )

        return anObject:init( ... )
end

http://dev.alt.textdrive.com/browser/lu/LUObject.lua


And subclasses are defined like this:

-- define the class
local super = LUObject
local self = super()

-- method for initialization
function self:init( aContent, aMode )
        self = super.init( self )

        if aMode ~= nil then
                setmetatable( self:content(), { __mode = aMode } )
        end

        self:addAll( aContent )

        return self
end

http://dev.alt.textdrive.com/browser/lu/LUList.lua


But... I don't bother with any of this anymore and simply use a 
combination of module and metamethods instead, e.g.:

module( 'URL' )
_VERSION = '1.0'

local self = setmetatable( _M, {} )
local meta = getmetatable( self )

function meta:__call( aValue )
    return NewURL( aValue )
end

function self:__add( aValue )
    return AddURLs( self, NewURL( aValue ) )
end

function self:__concat( aValue )
    return tostring( self ) .. tostring( aValue )
end

function self:__eq( aValue )
    return tostring( self ) == tostring( aValue )
end

function self:__lt( aValue )
    return tostring( self ) < tostring( aValue )
end

function self:__tostring()
    return WriteURL( self )
end

http://dev.alt.textdrive.com/browser/HTTP/URL.lua