If I have beginner Smalltalk questions. What is the best forum for asking those?
Here even if they aren't squeak specific? Some other mailing list?
"Sean" == Sean Allen sean@monkeysnatchbanana.com writes:
Sean> If I have beginner Smalltalk questions. What is the best forum for Sean> asking those?
Sean> Here even if they aren't squeak specific?
If you're learning Smalltalk by using Squeak, it makes sense to ask them here. If you're not using Squeak to learn, it might be best to start with an appropriate list for that vendor, simply because you might not know whether it's Squeak-specific or not.
On Aug 1, 2008, at 6:01 PM, Randal L. Schwartz wrote:
"Sean" == Sean Allen sean@monkeysnatchbanana.com writes:
Sean> If I have beginner Smalltalk questions. What is the best forum for Sean> asking those?
Sean> Here even if they aren't squeak specific?
If you're learning Smalltalk by using Squeak, it makes sense to ask them here. If you're not using Squeak to learn, it might be best to start with an appropriate list for that vendor, simply because you might not know whether it's Squeak-specific or not.
i'm using squeak but i also know they arent really squeak specific questions...
design type things like...
you have an instance variable you only want to allow to set once, never again ( in that fashion its like variable binding in erlang. ) what is the accepted smalltalk way to do this? is there one?
or
how are the equivalent of c++ virtual methods handled in smalltalk? what is the standard idiom for that design pattern?
those are two, i have more. is this the right forum? if not, where would be the right forum?
On Sat, Aug 02, 2008 at 12:08:51AM -0400, Sean Allen wrote:
you have an instance variable you only want to allow to set once, never again ( in that fashion its like variable binding in erlang. ) what is the accepted smalltalk way to do this? is there one?
ivar: aValue ivar ifNotNil: [self error: 'variable already set']. ^ ivar := aValue
how are the equivalent of c++ virtual methods handled in smalltalk? what is the standard idiom for that design pattern?
All methods in Smalltalk are virtual, i.e., looked up when called.
those are two, i have more. is this the right forum? if not, where would be the right forum?
Here or squeak-dev.
On Aug 2, 2008, at 12:44 AM, Matthew Fulmer wrote:
On Sat, Aug 02, 2008 at 12:08:51AM -0400, Sean Allen wrote:
you have an instance variable you only want to allow to set once, never again ( in that fashion its like variable binding in erlang. ) what is the accepted smalltalk way to do this? is there one?
ivar: aValue ivar ifNotNil: [self error: 'variable already set']. ^ ivar := aValue
so what i was doing is the correct way to do it.
how are the equivalent of c++ virtual methods handled in smalltalk? what is the standard idiom for that design pattern?
All methods in Smalltalk are virtual, i.e., looked up when called.
let me clarify that question.
if I have class foo that is meant to only be descended from, never instantiated directly. and it has method bar that needs to made concrete by its descendents, what is the standard idiom for that?
is there a specific error that should be thrown or just:
foo self error: 'any old error here'
is there a particular error that is common practice to use?
On Aug 2, 2008, at 10:43 AM, Sean Allen wrote:
if I have class foo that is meant to only be descended from, never instantiated directly. and it has method bar that needs to made concrete by its descendents, what is the standard idiom for that?
is there a specific error that should be thrown or just:
foo self error: 'any old error here'
is there a particular error that is common practice to use?
You can do
foo
self subclassResponsibility
in such cases.
Ben Schroeder
On Aug 2, 2008, at 10:50 AM, Benjamin Schroeder wrote:
On Aug 2, 2008, at 10:43 AM, Sean Allen wrote:
if I have class foo that is meant to only be descended from, never instantiated directly. and it has method bar that needs to made concrete by its descendents, what is the standard idiom for that?
is there a specific error that should be thrown or just:
foo self error: 'any old error here'
is there a particular error that is common practice to use?
You can do
foo
self subclassResponsibility
thanks ben. ok i have another. lets take something that in a sql driven environment would be a lookup table. countries and states. what the the smalltalk way with this?
ive come up with two basic ideas...
each country and each state/province is a single instance of their respective classes ( the class layout i can see a few different options but that isnt the thrust of the question. ). if its a single instance, then you have to deal with creation of each instance... how do you handle the instance creation? what is the normal method for setting up data to create them? monticello in the instances? have class side data that is used to build? this idea seems nice from being able to equality based on object equality but it seems like its generally overblown... however you could attach customized functionality easily if needed to different instances so that nice. ( in the past with C++, i would just load in data from a file on startup and create the objects the data file called for.... )
the other way i can see is to store all the information needed in class variables and create instances as needed when the are asked for. this seems much easier to manage but it feel less smalltalk. then again i dont really know what a smalltalk way really is, but a lookup data structure in class variables dont feel like it.
is one of these more smalltalk? is there something else more suited as a smalltalk solutuion? in the app i'm using to learn smalltak etc, i have this same basic pattern come up several times so I'd prefer to use the best method from the start so 3-6 months from now I dont have a 'o I should have done it this way because with smalltalk that allows... ' kind of moment.
Thanks to everyone for the help so far and any advice on tackling this.
Hi Sean,
ok i have another. lets take something that in a sql driven environment would be a lookup table. countries and states. what the the smalltalk way with this?
There are a number of patterns for this. Not all of them are strictly object oriented. The easiest way to do this is to use a database to hold and coordinate the data. Then you would query for the data and instantiate objects as needed (and maybe cache some frequently used ones).
Your suggestion of using a class variable or a class method that is responsible for creating all of your instances also makes sense. You can either build all the instances and save them in your image or build the instances during startup or lazily when needed. You need to have some root to hold those new instances to keep them from being garbage collected. This can also be done with a class variable. Just set a class variable to a collection of your instances, then use that variable to lookup your instances.
Having an external file is also a good way to go. The same issues arise from the file as for putting the data in a method, but benefit of using the file is that your data is not saved in code and can be updated without changing your running image, although your image needs to know when the file changes so that it can refresh your instances.
Hope that helps,
Ron Teitelbaum
beginners@lists.squeakfoundation.org
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Sean Allen