Empathy List Archives

D

danhunfeldz@mail.com

Mon, Dec 6, 2021 4:31 PM

Object subclass: #Test
    instanceVariableNames: 'var1 var2'
    classVariableNames: ''
    package: 'MyTest'

I was struggling with instanceVariableNames even though they show up under methods.  Perhaps I'm just slow, but it wasn't until last night when I was reading on Object Pascal and there was an example:

type
  TProjector = class(TTelevision)
    Brightness, Temperature: Integer;
    procedure Focus(Length: Single);
  end;

Then it finally clicked with me that "var1" and "var2" under instance variables in Smalltalk would be like the method "Focus" in Object Pascal.  Is that correct, or am I still not getting it?

``` Object subclass: #Test instanceVariableNames: 'var1 var2' classVariableNames: '' package: 'MyTest' I was struggling with instanceVariableNames even though they show up under methods. Perhaps I'm just slow, but it wasn't until last night when I was reading on Object Pascal and there was an example: type TProjector = class(TTelevision) Brightness, Temperature: Integer; procedure Focus(Length: Single); end; Then it finally clicked with me that "var1" and "var2" under instance variables in Smalltalk would be like the method "Focus" in Object Pascal. Is that correct, or am I still not getting it? ```

TT

Tomaž Turk

Mon, Dec 6, 2021 5:18 PM

Hi,

Instance variables are nicely explained in Pharo by Example in chapter
6.4 pp 89 http://books.pharo.org/.

Best wishes,
Tomaz

Hi, Instance variables are nicely explained in Pharo by Example in chapter 6.4 pp 89 http://books.pharo.org/. Best wishes, Tomaz

DG

duboismathieu_gaas@yahoo.fr

Wed, Dec 8, 2021 9:22 PM

I’m far from being an expert but I think you misunderstood. Are you familiar with the concept of instance variables and having trouble with the syntax or do you need some help on the concept of instance variables ?

Assuming you are familiar with the concept, here are some explanation about the syntax: in the Smalltalk example you gave, instance variables don’t show up in methods; this example is just the Smalltalk way to declare a class with two instance variables var1 and var2 (no method is declared here). The Pascal example would translate to:

TTelevision subclass: #Television
    instanceVariableNames: 'Brightness Temperature'
    classVariableNames: ''
    package: 'MyTest'

Methods like Focus are declared in a separate way.

If you are new to Smalltalk and OOP, I suggest you take the Pharo MOOC (https://www.fun-mooc.fr/en/courses/live-object-programming-pharo/) which will help you a lot.

HTH,
Mathieu

I’m far from being an expert but I think you misunderstood. Are you familiar with the concept of instance variables and having trouble with the syntax or do you need some help on the concept of instance variables ? Assuming you are familiar with the concept, here are some explanation about the syntax: in the Smalltalk example you gave, instance variables don’t show up in methods; this example is just the Smalltalk way to declare a class with two instance variables var1 and var2 (no method is declared here). The Pascal example would translate to: ``` TTelevision subclass: #Television instanceVariableNames: 'Brightness Temperature' classVariableNames: '' package: 'MyTest' ``` Methods like Focus are declared in a separate way. If you are new to Smalltalk and OOP, I suggest you take the Pharo MOOC (https://www.fun-mooc.fr/en/courses/live-object-programming-pharo/) which will help you a lot. HTH,\ Mathieu

RO

Richard O'Keefe

Wed, Dec 8, 2021 9:56 PM

If you are coming from a Pascal background,
instance variables of an object
correspond to
fields of a record.

They are called instance variables

because they are variables
that belong to INSTANCES of a class (object)
as opposed to class variables
which are variables
that belong to the CLASS itself and are thus
shared by all instances.

Other programming languages use terminology like slots,
fields, data members, ...

The keyword 'instanceVariableNames:' is used because the
string that follows contains the names of the variables,
not the variables themselves.

One thing to note is that in Smalltalk all instance
variables (fields, slots, whatever) are PRIVATE. These
are not the names of accessor methods, although there
may be accessor methods with the same spelling.

On Tue, 7 Dec 2021 at 05:32, danhunfeldz@mail.com wrote:

Object subclass: #Test
instanceVariableNames: 'var1 var2'
classVariableNames: ''
package: 'MyTest'

I was struggling with instanceVariableNames even though they show up under methods. Perhaps I'm just slow, but it wasn't until last night when I was reading on Object Pascal and there was an example:

type
TProjector = class(TTelevision)
Brightness, Temperature: Integer;
procedure Focus(Length: Single);
end;

Then it finally clicked with me that "var1" and "var2" under instance variables in Smalltalk would be like the method "Focus" in Object Pascal. Is that correct, or am I still not getting it?

If you are coming from a Pascal background, instance variables of an object correspond to fields of a record. They are called instance variables - because they are variables - that belong to INSTANCES of a class (object) as opposed to class variables - which are variables - that belong to the CLASS itself and are thus shared by all instances. Other programming languages use terminology like slots, fields, data members, ... The keyword 'instanceVariableNames:' is used because the string that follows contains the names of the variables, not the variables themselves. One thing to note is that in Smalltalk all instance variables (fields, slots, whatever) are PRIVATE. These are not the names of accessor methods, although there may be accessor methods with the same spelling. On Tue, 7 Dec 2021 at 05:32, <danhunfeldz@mail.com> wrote: > Object subclass: #Test > instanceVariableNames: 'var1 var2' > classVariableNames: '' > package: 'MyTest' > > I was struggling with instanceVariableNames even though they show up under methods. Perhaps I'm just slow, but it wasn't until last night when I was reading on Object Pascal and there was an example: > > type > TProjector = class(TTelevision) > Brightness, Temperature: Integer; > procedure Focus(Length: Single); > end; > > Then it finally clicked with me that "var1" and "var2" under instance variables in Smalltalk would be like the method "Focus" in Object Pascal. Is that correct, or am I still not getting it? > >

NH

Norbert Hartl

Thu, Dec 9, 2021 11:12 AM

Am 08.12.2021 um 22:56 schrieb Richard O'Keefe raoknz@gmail.com:

Other programming languages use terminology like slots,
fields, data members, ...

The keyword 'instanceVariableNames:' is used because the
string that follows contains the names of the variables,
not the variables themselves.

To experience that go into settings (under the „Pharo“ menu item) search for „slots“. You will get this

If you open a new system browser it looks like this

Collection << #SmallDictionary
slots: { #keys . #values . #size };
tag: 'Dictionaries';
package: 'Collections-Unordered‘

which resembles the slots representation better.

Hope this helps and not raise confusion even more.

Norbert

> Am 08.12.2021 um 22:56 schrieb Richard O'Keefe <raoknz@gmail.com>: > > Other programming languages use terminology like slots, > fields, data members, ... > > The keyword 'instanceVariableNames:' is used because the > string that follows contains the names of the variables, > not the variables themselves. To experience that go into settings (under the „Pharo“ menu item) search for „slots“. You will get this If you open a new system browser it looks like this Collection << #SmallDictionary slots: { #keys . #values . #size }; tag: 'Dictionaries'; package: 'Collections-Unordered‘ which resembles the slots representation better. Hope this helps and not raise confusion even more. Norbert

pharo-users@lists.pharo.org

InstanceVariables