RSS Feed

The Design of Software (CLOSED)

Hi,

I want to know how an object of a clas must be constructed which has some invariants?For example,itinerary specification is a class which when constructed..number of days must be > 0,client name should not be empty..now i normally hav done this was..
ItinearaSpec it=new ItinearaSpec
it.noofdays and it.clientname(both are set methods of properties,where i check if data is valid)eg
like
ItineraryDays
{
set{check if data is valid..if not then a boolean variable is set to true which indicates an invalid state and an event is raised to client}
}

But, Now i have been reading about immutable objects..and design by contract..i need some practical suggestions,and options?
thks
vishy

well if you are using C++ this is how you do it:

-decide what invariants you have
-make those variables private
-write a constructor for your class
-make sure that by the end of your constructor all invariants are satisfied
-create "set" methods that maintain the invariant

The key to success is establishing the invariant in the constructors

but if someone passes a value which is not satisfactory..what should i do in the constructor..raise an exception..or use a property to say invalid state..basically object should not be created..so shouldnt it be checked before calling a contructor..maybe a factory object..which will check if invariant criteria is met..and then create object??