From: Eric Schwartz <emschwar@...>
Date: 2003-05-01T07:38:29+09:00
Subject: Re: [OO interface design] Pass-by reference VS encapsulation ?

Simon Vandemoortele <deliriousREMOVEUPPERCASETEXTTOREPLY@atchoo.be> writes:
> Besides: what would happen if you call #save on a contact and the
> addressbook refuses the save because there's already an entry with that
> name ?

Hopefully, it wouldn't do that.  Or are you assuming you'll never meet
two people named Doug Jones?

> Wouldn't it be better if the Contact consulted the addressbook as
> soon as the duplicate name was entered ? (and not after all sorts of
> other attributes have been set on the contact)

Why should the Contact care if there's another object with the same
data it has?  It's the AddressBook's job to tell you things like
that.  One possible solution is to use an Observer pattern to allow
the AddressBook to register itself as being interested in operations
like changing names and optionally disallow them.  That way you can
pass around all the mutable object you like, and let the AddressBook
validate any prospective changes.

In this particular case, though, I'd invite you to look through a
phonebook of even a relatively small city and see how many duplicated
names there are.  Having some sort of unique key that is not a
person's name would be a better solution, IMO.

If you'd like to pass around an object and be sure it'll never get
altered by its reciever, then a Contact/MutableContact pair seems
unavoidable.

-=Eric
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