Geometry example

using DynamicObjects

"""
A common base type for shapes.
"""
@dynamic_type DynamicShape

description(what::DynamicShape) = "A $(what) has an area of $(what.area)."

"""
A fancy rectangle.
"""
@dynamic_object Rectangle <: DynamicShape height::Number width=1  
area(what::Rectangle) = what.height * what.width

"""
A boring circle.
"""
@dynamic_object Circle <: DynamicShape radius::Number
area(what::Circle) = what.radius^2 * pi 

println(Rectangle(10).description)
println(Circle(20).description)
Circle(20)  

DynamicObjects.cached(Circle(20), :area)

┌ Info: Precompiling DynamicObjects [23d02862-63fe-4c6e-8fdb-1d52cbbd39d5]
└ @ Base loading.jl:1664

A Rectangle(height = 10, width = 1) has an area of 10.
A Circle(radius = 20,) has an area of 1256.6370614359173.

1256.6370614359173