David Mitchell wrote:

I've seen both.

I try to avoid creating accessors and only add them as I need. I try to create methods based on the responsibilities of the object and not around its data structure.

But, I've worked on projects where every object had accessors for every variable (often necessitated by the persistence framework). You have to trust the programmers not to abuse them as a simple data structure.

Kent Beck's Smalltalk Best Practice Patterns describes the forces behind each approach.

Another reason to use accessors is lazy initialization.

I think this is actually the best reason:

myVar

"return state of myVar. if nil, initialize with default value"

myVar isNil ifTrue:[myVar := myClass defaultValue]. ^myVar

If you have to pay attention to variable initialisation, you have to do it somewhere. So, if you have your own domain model objects, you can do it in #initialize (or #new, if you are adventurous).

If you do not have classes for your own objects, i.e. if your instance variables are Strings/Collections/whatever, then you have to do it somewhere else, but where? In #new or #initialize of the class containing the instance variables? Or even in a factory method?

That can lead to a lot of code, hence confusion.

Personally, I favour lazy initalisation, due to the pseudo-encapsulation (if I may misuse the term here) it offers (whatever the variable is, it will have a meaningful value after accessing it the first time) but that is just my opinion.

Claus