[self-interest] Re: simple object model
Jecel Assumpcao Jr
jecel at merlintec.com
Fri Apr 6 22:07:03 UTC 2001
On Friday 06 April 2001 13:25, Uladzimir Liashkevich wrote:
> > ... ^ ( (| x. y |) x: sX) y: sY
> It looks much better.
> Idea! Not I know what I actually wanted:
> prototypes point copyWith: (x 3 y 4)
> I.e. initializing an object with a hash.
> The copyWith: method can be easily implemented in Self, but it misses
> literal hashes (more importantly, initialized at run-time).
Like I said to Steve, I don't really see any difference between current
Self objects and hash tables. You could implement the 'copyWith:'
method so that you can write
prototypes point copyWith: (| x=3. y=4 |)
If you wanted sX and sY instead of 3 and 4, then you would need a
complex unquoting notation like some languages have. Though Self has
literal objects (like in the above example), it lacks a syntax for
literal arrays and other things. The closest we have is the use of
( 1 & 1 & 2 & 3 & 5 & 8 & 13 & 21 ) asVector
#( 1 1 2 3 5 8 13 21 )
But since it is an expression that builds the object at runtime, you
can replace the numbers above by any expression in Self but it becomes
complicated in Smalltalk.
Rebol has a rich set of literal object syntaxes, but I think this is
something that only makes sense in a purely text based languages. As
our programming environment becomes more and more graphical, I would
rather create my literal objects with some proper tool and just drop it
in the middle of my code. After all, though I can't show this in an
ASCII email (but could do so in a HTML one), it would be nicer to see
currentCursor: <image of hourglass>
That is also my opinion about Scheme-like macros. Penny wise, pound
foolish. They are trying to make more readable things we shouldn't have
> > [do we actually gain anything by making
> > parents visible at the base level?]
> For example, hierarchies of traits/prototypes.
> Also for eliminating ambiguities:
> globals app1 myObject
> globals app2 myObject
These are regular data slots, not parent slots. About
traits/prototypes, you do have a point in that we get to reuse the slot
initializer syntax for setting the inheritance relationships. But that
is not important in a GUI environment, only a pure text one.
> At first glance I liked the idea of declaring maps, but now I see
> some drawbacks here. The main is that the notation is
> position-dependant, i.e. if later you want to add another slot to the
> map - (x : x1 : y :), you should carefully keep track of positions in
> the list of slot initializers - ((x : x1 : y :) 3 10 4). But what if
> the number of slots is very high?
> IMHO, it is an error-prone construction.
There are plenty of problems with this idea. But you wouldn't have to
manipulate objects at this level directly - there should be graphical
tools to take care of the details and get things right.
> In my implementations I have a hidden object with all primitive
> slots. When a message name begins with underscore then a lookup is
> performed in the hidden object.
My problem with this is that it isn't very object oriented. If you do
someObj _PrimXWith: n
then '_PrimXWith:' is actually a global function (with someObj and n as
arguments) and not and method. So much so that if someObj is not what
the primitive was expecting you get an "invalid receiver type" error
and not a "does not understand" error.
Of course, you can think of your hidden object as representing the
virtual machine. It is just that I don't like one giant object doing
everything by itself.
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