--[[
Moving towards Lua objects - Metatables
]]

-- Define the methods for a Couple
-- A new Couple is a couple in a metatable "mtab"

Couple = {}
local mtab = {}

-- How to create them
function Couple.new(him, her)
        local current = {}
        setmetatable(current,mtab)
        current.him = him
        current.her = her
        return current
        end

-- How to perform an operation on them
function Couple.diff(current)
        local diff = current.him - current.her
        if diff < 0 then diff = - diff end
        return diff
        end

-- How to add them
function Couple.combine(first, second)
        local combo = Couple.new(
                first.him + second.him,
                first.her + second.her)
        return combo
        end

-- How to turn them into a print string
function Couple.print(current)
        local str = "He is " .. current.him ..
                " and she is " .. current.her
        return str
        end

mtab.__add = Couple.combine

mtab.__lt = function (one, two)
        local sm1 = one.him + one.her
        local sm2 = two.him + two.her
        return sm1 < sm2 and true or false
        end

mtab.__tostring = Couple.print

mtab.__index = function( item, key)
        if key == "hisage" then return item.him end
        if key == "herage" then return item.her end
        return nil
        end

----------------------------------------
-- Create a pair of couples ...

thems = Couple.new(55,47)
youngs = Couple.new(28,30)

print ("\nPrinting from a table")
print (Couple.print(thems))
print ("Using tostring and __add")
print(youngs)
print (thems + youngs)

print ("\n running a function on an object")
print (Couple.diff(thems))
print (Couple.diff(youngs))

print ("\ncomparing tables / objects")
if thems < youngs then
        print "Apricot"
else
        print "Banana"
end

if youngs < thems then
        print "Cherry"
else
        print "Pineapple"
end

print ("\ncalling __index to access properties")
print (thems.hisage)
print (youngs.herage)

--[[ ----------------------- Sample Output ---------------

[trainee@easterton u107]$ lua couples

Printing from a table
He is 55 and she is 47
Using tostring and __add
He is 28 and she is 30
He is 83 and she is 77

 running a function on an object
8
2

comparing tables / objects
Banana
Cherry

calling __index to access properties
55
30
[trainee@easterton u107]$

]]