[squeak-dev] Object>>printOn: refined.

Marcel Taeumel marcel.taeumel at hpi.de
Wed Jun 3 08:24:08 UTC 2020

Hi Chris.

> Seeing just their identifications removes a level of formality that seems to foster a better UI "connection" to the objects.

Domain-specific objects can provide a good-enough identification in their #printOn: specialization. Maybe the class name is part of it. Maybe not. If you develop a database, for example, you surely have another notion of identity. Meaning, other than Object >> #identityhash or #oop. That other notion of (compact) identity should then be part of an object's print-string that is part of the database.

Yet, nothing one can foresee, when thinking about Object >> #printOn:. There, you have only the meta-object protocol at hand: class name, identity hash, maybe ref counter? :-D Having a new subclass of Object, what should that #printOn: look like out-of-the-box? The class name is fine. So you can actually see that your new class' instances are populating the world. Next step should be to implement a custom #printOn: in that new class.

Am 03.06.2020 05:16:31 schrieb Chris Muller <asqueaker at gmail.com>:
Hi Trygve,

Of all the attributes that objects print, I find the "type" (class) to be one of the least interesting.  It's usually already obvious in its contextual usage.  Indeed, it is the "identity" that I, too, am interested in seeing printed.  My solution since 2006 has been an override of #printOn: that adds a one-line dispatch to #printIdentificationOn:.  I then take care in my #printIdentificationOn: implementations to keep the printing as terse as it can be, and sans any line endings, to serve this seemingly recurring use-case I have of wanting a "short version" of an object's string.  For example, when printing the elements of a collection.  Having entire domain hierarchies exclude the type entirely from their printString's has been a fantastic experience.  Seeing just their identifications removes a level of formality that seems to foster a better UI "connection" to the objects.


On Tue, Jun 2, 2020 at 7:10 AM Trygve Reenskaug <trygver at ifi.uio.no [mailto:trygver at ifi.uio.no]> wrote:

I find it frustrating to open 3 inspectors on different objects, all of them titled 'aString' (or whatever),
IMO, it is much better to open them on the 3 objects: [1234] aString, [3456] a String, [4567 a String.
The numbers in square brackets stand for the objects oop, actually its identityHash. They can be a 7-digit numbers; much too long for my short-time memory to hold many of them. I therefore truncate the number to 4 digits, accepting that I may, in rare cases, get 2 objects with the same identifier.

I'm running 'Squeak5.3'.
Object>>printOn: aStream
        "Append to the argument, aStream, a sequence of characters that identifies the receiver."
        " The previous version identified the class, not the instance "
        " This new version identifies the instance with its oop. "
        " I arbitrarily truncate the oop to 4 digits to simplify reading. "

        | title |
        title := self class name.
            nextPutAll: '[' , (self asOop printString truncateTo: 4) , ']' ;
            nextPutAll: (title first isVowel ifTrue: ['an '] ifFalse: ['a ']);
            nextPutAll: title



The essence of object orientation is that objects collaborate  to achieve a goal.
Trygve Reenskaug      mailto: trygver at ifi.uio.no [mailto:%20trygver at ifi.uio.no]
Morgedalsvn. 5A       http://folk.uio.no/trygver/ [http://folk.uio.no/trygver/]
N-0378 Oslo             http://fullOO.info [http://fullOO.info]
Norway                     Tel: (+47) 468 58 625
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