Blaine Buxton: Positronic Vibrations From Alto Dorado

I was reading a paper entitled, "Objectoriented Encapsulation for Dynamically Typed Languages", and came across an interesting piece of information.

Some Smalltalk dialects attempt to solve this problem by using a special naming convention to specify internal methods. In the Squeak dialect, for example, methods whose names begin with pvt are effectively private: the compiler ensures that these messages can be sent only to self. However, this approach not only prevents accesses to such internal methods from outside of their class but also from other objects of the same class. Thus, the pvt convention is a form
of object encapsulation: in practice it is often too strict, because it prevents many commonly used data structures and patterns from being implemented. As with Python’s double underscore, this approach is clumsy because changing the access attributes of a method requires renaming it.

Huh? I've been using Squeak for a little while now and never knew of this feature. I even asked my good friend and fellow Squeaker, Steve Wessels, about it. He told me that he had never heard of it. The paper continues with this nugget:

The utility of the pvt feature is reflected in the Squeak image: although this feature has been available for years, only 9 out of about 40,000 methods in the latest Squeak image use it.

OK, I had to go check this out, so I fired up my trusy 3.8 image and did the following:

| result |
result := OrderedCollection new.
RTCriteria new 
 methodsWhere: 
  [:each | 
   each beginsWith: 'pvt'];
 methodsDo: 
  [:eachClass :eachMethod |
   result add: (eachClass -> eachMethod)].
result

I got a result of 31 methods. Some of those come from Komanche and Celeste which are not part of the base image. Still, how come I never found about this? Squeak is just full of little nuggets. I'm constantly uncovering little things like this.

It's something new for me to try out and see how I like it. I've been an extreme encapsulation kick as of late and this is just adding fuel to my fire. I don't like adding pvt to the front, but it makes it painfully obvious when I'm breaking the rules and things like the refactoring browser help when I decide to change my mind.

So, I wonder what other little surprises are out there still waiting for me? Squeak is a surprise a minute! Oh yeah, the paper is an excellent read and I highly recommend it. I'm going to have to try out the stuff in it as well.

posted by Blaine at 11:38 PM |  0 comments |  Post a Comment