local math = require("math")

-- We'll use a table to represent our "interface"
local geometry = {}

-- Rectangle implementation
local rect = {}
rect.__index = rect

function rect.new(width, height)
    return setmetatable({width = width, height = height}, rect)
end

function rect:area()
    return self.width * self.height
end

function rect:perim()
    return 2 * self.width + 2 * self.height
end

-- Circle implementation
local circle = {}
circle.__index = circle

function circle.new(radius)
    return setmetatable({radius = radius}, circle)
end

function circle:area()
    return math.pi * self.radius * self.radius
end

function circle:perim()
    return 2 * math.pi * self.radius
end

-- A generic function to measure any "geometry" object
local function measure(g)
    print(g)
    print(g:area())
    print(g:perim())
end

-- Main function
local function main()
    local r = rect.new(3, 4)
    local c = circle.new(5)

    -- We can use instances of rect and circle as arguments to measure
    measure(r)
    measure(c)
end

main()