How can I make this more OOP
Hi Roelof, Polymorphism is the answer. Object >> flattenInto: result result nextPut: anObject UndefinedObject >> flattenInto: result ^self Collection >> flattenInto: result self do: [ :item | item flattenInto: result ] flatten: anObject ^ (OrderedCollection streamContents: [ :stream | anObject flattenInto: stream ]) asArray Noury
On 13 Sep 2020, at 11:26, Roelof Wobben via Pharo-users <pharo-users@lists.pharo.org> wrote:
Hello,
I know that OOP is not asking a object what it is but I have to flatten a array so I did this :
flattenArray: aCollection ^ (OrderedCollection streamContents: [ :stream | self flatten: aCollection into: stream ]) asArray
flatten: anObject into: result ^ anObject isCollection ifTrue: [ anObject do: [ :item | self flatten: item into: result ] ] ifFalse: [ anObject ifNotNil: [ result nextPut: anObject ] ]
The name flattenArray is given bij exercism.
Now I wonder how I can make this more a OOP solution.
Can someone give me some hints or some examples ?
Roelof
"OOP is not asking an object what it is"? You've lost me. I'm reminded of a joke exam question that goes something like this: Some things have ping nature and other things have pong nature. Discuss, with examples. Whatever else it is, OOP is a means to an end, not an end in itself. It's not a religion. Allah will not cast you into the Fire for using something which is not ritually pure. The whole point of the Design Patterns movement was not to present canned solutions but to describe common *situations* characterised by (metaphorical) *forces* pushing you in incompatible directions. Question 1: Why do you even have a stream there? flattenArray: aCollection |buffer| buffer := OrderedCollection new: aCollection size. self flattenArray: aCollection into: buffer. ^buffer asArray flattenArray: anObject into: buffer (anObject respondsTo: #do:) ifTrue: [anObject do: [:each | self flattenArray: each into: buffer] ifFalse: [anObject ifNotNil: [buffer addLast: anObject]. (CAUTION: untested code.) Question 2: is there any point in *trying* to make this more ping and less pong? I have to say that in 40 years of programming, I have *never* wanted to flatten a completely arbitrary structure. When I have wanted to flatten something, it has always been an instance of the Composite design pattern, so that a specific and quite small set of classes has been involved. I am well aware that some Smalltalk systems have some sort of 'flatten' lying around like a rake in the grass, but I have found no two which agree on the specification. Question 3: Let's consider an if-less alternative. Stream flattenInto: buffer self do: [:each| each flattenInto: buffer]. Collection flattenInto: buffer self do:[:each | each flattenInto: buffer]. Object flattenInto: buffer buffer addLast: self. UndefinedObject flattenInto: buffer "Do nothing." This is Smalltalk, where we *can* add methods to system classes like these. When the payoff is worth it, I have no qualms whatever in doing so. But putting methods of little or no utility into the interface of EVERY object just feels so wrong. Here we have opposing forces: - The first approach adds two methods to your worker class, and no methods to any system class. Instead, it uses "does this object know how to iterate over its elements?" and "is this object nil?". This does minimal damage to system structure at the price of a little ritual impurity. - The second approach adds a method to four system classes, enlarging the interface of every object in the system, creating a level of coupling we'd be better without, and making it harder for someone reading your code to figure out what's going on. In the context of a Composite, with a limited number of application classes involved, the second approach is better; the method is/methods are not defined anywhere they should not be. In the context of *this* problem, the first approach is better. MUCH better. Why? Because *encapsulation* is much more important to OOP than absence-of-IFs. On Sun, 13 Sep 2020 at 21:26, Roelof Wobben via Pharo-users < pharo-users@lists.pharo.org> wrote:
Hello,
I know that OOP is not asking a object what it is but I have to flatten a array so I did this :
flattenArray: aCollection ^ (OrderedCollection streamContents: [ :stream | self flatten: aCollection into: stream ]) asArray
flatten: anObject into: result ^ anObject isCollection ifTrue: [ anObject do: [ :item | self flatten: item into: result ] ] ifFalse: [ anObject ifNotNil: [ result nextPut: anObject ] ]
The name flattenArray is given bij exercism.
Now I wonder how I can make this more a OOP solution.
Can someone give me some hints or some examples ?
Roelof
On 14 Sep 2020, at 16:02, Roelof Wobben via Pharo-users <pharo-users@lists.pharo.org> wrote:
Thanks Richard for this explanation. and I like also your idea of using #respondTo instead of asking a object if its a collection or a item.
refrain from using respondTo: I make code difficult to evolve and can introduce vicious bugs. S.
Roelof
Op 14-9-2020 om 14:28 schreef Richard O'Keefe:
"OOP is not asking an object what it is"? You've lost me. I'm reminded of a joke exam question that goes something like this: Some things have ping nature and other things have pong nature. Discuss, with examples.
Whatever else it is, OOP is a means to an end, not an end in itself. It's not a religion. Allah will not cast you into the Fire for using something which is not ritually pure.
The whole point of the Design Patterns movement was not to present canned solutions but to describe common *situations* characterised by (metaphorical) *forces* pushing you in incompatible directions.
Question 1: Why do you even have a stream there? flattenArray: aCollection |buffer| buffer := OrderedCollection new: aCollection size. self flattenArray: aCollection into: buffer. ^buffer asArray
flattenArray: anObject into: buffer (anObject respondsTo: #do:) ifTrue: [anObject do: [:each | self flattenArray: each into: buffer] ifFalse: [anObject ifNotNil: [buffer addLast: anObject].
(CAUTION: untested code.)
Question 2: is there any point in *trying* to make this more ping and less pong? I have to say that in 40 years of programming, I have *never* wanted to flatten a completely arbitrary structure. When I have wanted to flatten something, it has always been an instance of the Composite design pattern, so that a specific and quite small set of classes has been involved.
I am well aware that some Smalltalk systems have some sort of 'flatten' lying around like a rake in the grass, but I have found no two which agree on the specification.
Question 3: Let's consider an if-less alternative.
Stream flattenInto: buffer self do: [:each| each flattenInto: buffer].
Collection flattenInto: buffer self do:[:each | each flattenInto: buffer].
Object flattenInto: buffer buffer addLast: self.
UndefinedObject flattenInto: buffer "Do nothing."
This is Smalltalk, where we *can* add methods to system classes like these. When the payoff is worth it, I have no qualms whatever in doing so. But putting methods of little or no utility into the interface of EVERY object just feels so wrong.
Here we have opposing forces: - The first approach adds two methods to your worker class, and no methods to any system class. Instead, it uses "does this object know how to iterate over its elements?" and "is this object nil?". This does minimal damage to system structure at the price of a little ritual impurity.
- The second approach adds a method to four system classes, enlarging the interface of every object in the system, creating a level of coupling we'd be better without, and making it harder for someone reading your code to figure out what's going on.
In the context of a Composite, with a limited number of application classes involved, the second approach is better; the method is/methods are not defined anywhere they should not be.
In the context of *this* problem, the first approach is better. MUCH better. Why? Because *encapsulation* is much more important to OOP than absence-of-IFs.
On Sun, 13 Sep 2020 at 21:26, Roelof Wobben via Pharo-users <pharo-users@lists.pharo.org <mailto:pharo-users@lists.pharo.org>> wrote: Hello,
I know that OOP is not asking a object what it is but I have to flatten a array so I did this :
flattenArray: aCollection ^ (OrderedCollection streamContents: [ :stream | self flatten: aCollection into: stream ]) asArray
flatten: anObject into: result ^ anObject isCollection ifTrue: [ anObject do: [ :item | self flatten: item into: result ] ] ifFalse: [ anObject ifNotNil: [ result nextPut: anObject ] ]
The name flattenArray is given bij exercism.
Now I wonder how I can make this more a OOP solution.
Can someone give me some hints or some examples ?
Roelof
-------------------------------------------- Stéphane Ducasse http://stephane.ducasse.free.fr / http://www.pharo.org 03 59 35 87 52 Assistant: Aurore Dalle FAX 03 59 57 78 50 TEL 03 59 35 86 16 S. Ducasse - Inria 40, avenue Halley, Parc Scientifique de la Haute Borne, Bât.A, Park Plaza Villeneuve d'Ascq 59650 France
In a language like Java or C# or Ada we can insist at compile time that an argument conforms to a protocol, whatever class it might be an instance of. In Smalltalk, we can use #isKindOf: to test whether an object inherits from a class, but that is often the wrong test. We can use (multiple calls to) #respondsTo: to tell whether an object conforms to a protocol. The only snag, of course, is that in too many Smalltalk systems, #respondsTo: is not trustworthy. If a class has a method that sends #subclassResponsibility or #shouldNotImplement, it's still counted as responding to the selector in question. This is not a problem in my Smalltalk because (a) you are not allowed to create a direct instance of a class where any method calls #subclassResponsibility. (b) #shouldNotImplement appears only in test cases. Since I already have named protocols, with classes declaring their intention to conform to them, I've been thinking about adding aClass implements: aProtocol anInstance conformsTo: aProtocol but have not done that yet. I note that Pharo V7.0.3 had 132 senders of #respondsTo: and Pharo V8.0.0 has 126 senders of #respondsTo:. These neatly bracket Dolphin 7's 130. On Wed, 16 Sep 2020 at 06:50, Stéphane Ducasse <stephane.ducasse@inria.fr> wrote:
On 14 Sep 2020, at 16:02, Roelof Wobben via Pharo-users < pharo-users@lists.pharo.org> wrote:
Thanks Richard for this explanation. and I like also your idea of using #respondTo instead of asking a object if its a collection or a item.
refrain from using respondTo: I make code difficult to evolve and can introduce vicious bugs.
S.
Roelof
Op 14-9-2020 om 14:28 schreef Richard O'Keefe:
"OOP is not asking an object what it is"? You've lost me. I'm reminded of a joke exam question that goes something like this: Some things have ping nature and other things have pong nature. Discuss, with examples.
Whatever else it is, OOP is a means to an end, not an end in itself. It's not a religion. Allah will not cast you into the Fire for using something which is not ritually pure.
The whole point of the Design Patterns movement was not to present canned solutions but to describe common *situations* characterised by (metaphorical) *forces* pushing you in incompatible directions.
Question 1: Why do you even have a stream there? flattenArray: aCollection |buffer| buffer := OrderedCollection new: aCollection size. self flattenArray: aCollection into: buffer. ^buffer asArray
flattenArray: anObject into: buffer (anObject respondsTo: #do:) ifTrue: [anObject do: [:each | self flattenArray: each into: buffer] ifFalse: [anObject ifNotNil: [buffer addLast: anObject].
(CAUTION: untested code.)
Question 2: is there any point in *trying* to make this more ping and less pong? I have to say that in 40 years of programming, I have *never* wanted to flatten a completely arbitrary structure. When I have wanted to flatten something, it has always been an instance of the Composite design pattern, so that a specific and quite small set of classes has been involved.
I am well aware that some Smalltalk systems have some sort of 'flatten' lying around like a rake in the grass, but I have found no two which agree on the specification.
Question 3: Let's consider an if-less alternative.
Stream flattenInto: buffer self do: [:each| each flattenInto: buffer].
Collection flattenInto: buffer self do:[:each | each flattenInto: buffer].
Object flattenInto: buffer buffer addLast: self.
UndefinedObject flattenInto: buffer "Do nothing."
This is Smalltalk, where we *can* add methods to system classes like these. When the payoff is worth it, I have no qualms whatever in doing so. But putting methods of little or no utility into the interface of EVERY object just feels so wrong.
Here we have opposing forces: - The first approach adds two methods to your worker class, and no methods to any system class. Instead, it uses "does this object know how to iterate over its elements?" and "is this object nil?". This does minimal damage to system structure at the price of a little ritual impurity.
- The second approach adds a method to four system classes, enlarging the interface of every object in the system, creating a level of coupling we'd be better without, and making it harder for someone reading your code to figure out what's going on.
In the context of a Composite, with a limited number of application classes involved, the second approach is better; the method is/methods are not defined anywhere they should not be.
In the context of *this* problem, the first approach is better. MUCH better. Why? Because *encapsulation* is much more important to OOP than absence-of-IFs.
On Sun, 13 Sep 2020 at 21:26, Roelof Wobben via Pharo-users < pharo-users@lists.pharo.org> wrote:
Hello,
I know that OOP is not asking a object what it is but I have to flatten a array so I did this :
flattenArray: aCollection ^ (OrderedCollection streamContents: [ :stream | self flatten: aCollection into: stream ]) asArray
flatten: anObject into: result ^ anObject isCollection ifTrue: [ anObject do: [ :item | self flatten: item into: result ] ] ifFalse: [ anObject ifNotNil: [ result nextPut: anObject ] ]
The name flattenArray is given bij exercism.
Now I wonder how I can make this more a OOP solution.
Can someone give me some hints or some examples ?
Roelof
-------------------------------------------- Stéphane Ducasse http://stephane.ducasse.free.fr / http://www.pharo.org 03 59 35 87 52 Assistant: Aurore Dalle FAX 03 59 57 78 50 TEL 03 59 35 86 16 S. Ducasse - Inria 40, avenue Halley, Parc Scientifique de la Haute Borne, Bât.A, Park Plaza Villeneuve d'Ascq 59650 France
still my point holds. And Iâm like saint christophe I only believe what I saw and we will never see what you are doing so it does not exist. This is the rule of open-source. S.
On 16 Sep 2020, at 04:51, Richard O'Keefe <raoknz@gmail.com> wrote:
In a language like Java or C# or Ada we can insist at compile time that an argument conforms to a protocol, whatever class it might be an instance of.
In Smalltalk, we can use #isKindOf: to test whether an object inherits from a class, but that is often the wrong test. We can use (multiple calls to) #respondsTo: to tell whether an object conforms to a protocol.
The only snag, of course, is that in too many Smalltalk systems, #respondsTo: is not trustworthy. If a class has a method that sends #subclassResponsibility or #shouldNotImplement, it's still counted as responding to the selector in question.
This is not a problem in my Smalltalk because (a) you are not allowed to create a direct instance of a class where any method calls #subclassResponsibility. (b) #shouldNotImplement appears only in test cases. Since I already have named protocols, with classes declaring their intention to conform to them, I've been thinking about adding aClass implements: aProtocol anInstance conformsTo: aProtocol but have not done that yet.
I note that Pharo V7.0.3 had 132 senders of #respondsTo: and Pharo V8.0.0 has 126 senders of #respondsTo:. These neatly bracket Dolphin 7's 130.
On Wed, 16 Sep 2020 at 06:50, Stéphane Ducasse <stephane.ducasse@inria.fr <mailto:stephane.ducasse@inria.fr>> wrote:
On 14 Sep 2020, at 16:02, Roelof Wobben via Pharo-users <pharo-users@lists.pharo.org <mailto:pharo-users@lists.pharo.org>> wrote:
Thanks Richard for this explanation. and I like also your idea of using #respondTo instead of asking a object if its a collection or a item.
refrain from using respondTo: I make code difficult to evolve and can introduce vicious bugs.
S.
Roelof
Op 14-9-2020 om 14:28 schreef Richard O'Keefe:
"OOP is not asking an object what it is"? You've lost me. I'm reminded of a joke exam question that goes something like this: Some things have ping nature and other things have pong nature. Discuss, with examples.
Whatever else it is, OOP is a means to an end, not an end in itself. It's not a religion. Allah will not cast you into the Fire for using something which is not ritually pure.
The whole point of the Design Patterns movement was not to present canned solutions but to describe common *situations* characterised by (metaphorical) *forces* pushing you in incompatible directions.
Question 1: Why do you even have a stream there? flattenArray: aCollection |buffer| buffer := OrderedCollection new: aCollection size. self flattenArray: aCollection into: buffer. ^buffer asArray
flattenArray: anObject into: buffer (anObject respondsTo: #do:) ifTrue: [anObject do: [:each | self flattenArray: each into: buffer] ifFalse: [anObject ifNotNil: [buffer addLast: anObject].
(CAUTION: untested code.)
Question 2: is there any point in *trying* to make this more ping and less pong? I have to say that in 40 years of programming, I have *never* wanted to flatten a completely arbitrary structure. When I have wanted to flatten something, it has always been an instance of the Composite design pattern, so that a specific and quite small set of classes has been involved.
I am well aware that some Smalltalk systems have some sort of 'flatten' lying around like a rake in the grass, but I have found no two which agree on the specification.
Question 3: Let's consider an if-less alternative.
Stream flattenInto: buffer self do: [:each| each flattenInto: buffer].
Collection flattenInto: buffer self do:[:each | each flattenInto: buffer].
Object flattenInto: buffer buffer addLast: self.
UndefinedObject flattenInto: buffer "Do nothing."
This is Smalltalk, where we *can* add methods to system classes like these. When the payoff is worth it, I have no qualms whatever in doing so. But putting methods of little or no utility into the interface of EVERY object just feels so wrong.
Here we have opposing forces: - The first approach adds two methods to your worker class, and no methods to any system class. Instead, it uses "does this object know how to iterate over its elements?" and "is this object nil?". This does minimal damage to system structure at the price of a little ritual impurity.
- The second approach adds a method to four system classes, enlarging the interface of every object in the system, creating a level of coupling we'd be better without, and making it harder for someone reading your code to figure out what's going on.
In the context of a Composite, with a limited number of application classes involved, the second approach is better; the method is/methods are not defined anywhere they should not be.
In the context of *this* problem, the first approach is better. MUCH better. Why? Because *encapsulation* is much more important to OOP than absence-of-IFs.
On Sun, 13 Sep 2020 at 21:26, Roelof Wobben via Pharo-users <pharo-users@lists.pharo.org <mailto:pharo-users@lists.pharo.org>> wrote: Hello,
I know that OOP is not asking a object what it is but I have to flatten a array so I did this :
flattenArray: aCollection ^ (OrderedCollection streamContents: [ :stream | self flatten: aCollection into: stream ]) asArray
flatten: anObject into: result ^ anObject isCollection ifTrue: [ anObject do: [ :item | self flatten: item into: result ] ] ifFalse: [ anObject ifNotNil: [ result nextPut: anObject ] ]
The name flattenArray is given bij exercism.
Now I wonder how I can make this more a OOP solution.
Can someone give me some hints or some examples ?
Roelof
-------------------------------------------- Stéphane Ducasse http://stephane.ducasse.free.fr <http://stephane.ducasse.free.fr/> / http://www.pharo.org <http://www.pharo.org/> 03 59 35 87 52 Assistant: Aurore Dalle FAX 03 59 57 78 50 TEL 03 59 35 86 16 S. Ducasse - Inria 40, avenue Halley, Parc Scientifique de la Haute Borne, Bât.A, Park Plaza Villeneuve d'Ascq 59650 France
-------------------------------------------- Stéphane Ducasse http://stephane.ducasse.free.fr / http://www.pharo.org 03 59 35 87 52 Assistant: Aurore Dalle FAX 03 59 57 78 50 TEL 03 59 35 86 16 S. Ducasse - Inria 40, avenue Halley, Parc Scientifique de la Haute Borne, Bât.A, Park Plaza Villeneuve d'Ascq 59650 France
Stéphane Ducasse <stephane.ducasse@inria.fr> wrote:
refrain from using respondTo: I make code difficult to evolve and can introduce vicious bugs.
Steph, would you say more about this? Itâs something Iâve been wondering about. I was recently reading the Strategy pattern in the Smalltalk Companion to the GOF book. On p. 339, they proposed the following "Smalltalk way" as an alternative to the common class-per-strategy implementation: \[\[\[language=smalltalk Composition>>repair "Without the strategy pattern, but using perform:." | selector | "Construct the name of the method to invoke:" selector := ('formatWith', formattingStrategy, 'Algorithm') asSymbol. self perform: selector \]\]\] It then dismissed the approach as "''clever but difficult from a program understanding perspective. Even static analysis tools such as code browsers' "senders" and "messages" fail on this code.''" It struck me as perhaps a bit extreme (i.e. too clever indeed) to construct the algorithm selector via string concatenation. Maybe "senders" search capabilities have gotten more sophisticated since publication, but Pharo seems to support symbol arguments, even for e.g. message renames. I thought, why not the following: \[\[\[language=smalltalk Composition>>repair "Without the strategy pattern, but using perform:." self perform: self formattingStrategy \]\]\] Then client code like ==aComposition formattingStrategy: #formatWithSimpleAlgorithm== would show up in senders, message renames, etc. But from what youâre saying, I feel I may be missing somethingâ¦
On Wed, Sep 16, 2020 at 10:28 AM <sean@clipperadams.com> wrote:
Stéphane Ducasse <stephane.ducasse@inria.fr> wrote:
refrain from using respondTo: I make code difficult to evolve and can introduce vicious bugs.
Steph, would you say more about this? Itâs something Iâve been wondering about.
I was recently reading the Strategy pattern in the Smalltalk Companion to the GOF book. On p. 339, they proposed the following "Smalltalk way" as an alternative to the common class-per-strategy implementation:
[[[language=smalltalk
Composition>>repair
"Without the strategy pattern, but using perform:."
| selector |
"Construct the name of the method to invoke:"
selector := ('formatWith', formattingStrategy, 'Algorithm') asSymbol.
self perform: selector
]]]
It then dismissed the approach as "''clever but difficult from a program understanding perspective. Even static analysis tools such as code browsers' "senders" and "messages" fail on this code.''"
It is always best to have senders of the methods you use. Additionally, it's far better to properly manage the user-friendly identification of a thing and the thing itself. e.g. Plain language name mapped to a selector or a block. Remember, "the fact that one *can* do something is far different from whether one *should* do that thing." (I have suffered far too often and far too long from clever programs preferring the former without thinking about the latter.) It struck me as perhaps a bit extreme (i.e. too clever indeed) to construct
the algorithm selector via string concatenation. Maybe "senders" search capabilities have gotten more sophisticated since publication, but Pharo seems to support symbol arguments, even for e.g. message renames. I thought, why not the following:
[[[language=smalltalk
Composition>>repair
"Without the strategy pattern, but using perform:."
self perform: self formattingStrategy
]]]
Then client code like ==aComposition formattingStrategy: #formatWithSimpleAlgorithm== would show up in senders, message renames, etc.
But from what youâre saying, I feel I may be missing somethingâ¦
respondTo: is different from a perform based on forging a selector. respondTo: implies a different control while perform: is just sending a message. Some logic of Spec or something else was doing respondTo: and it is an indication of weak polymorphism. Either objects are polymorphic or they are not. Because else you expect a behavior and because of a hidden respondTo: you get a api not invoked. This forces you to read all the code and step to find the super cool users of respondTo: So I really stand on my claim respondTo: should only be used in last resort. It covers shitty design. S.
On 16 Sep 2020, at 19:28, sean@clipperadams.com wrote:
Stéphane Ducasse <stephane.ducasse@inria.fr> wrote:
refrain from using respondTo: I make code difficult to evolve and can introduce vicious bugs.
Steph, would you say more about this? Itâs something Iâve been wondering about.
I was recently reading the Strategy pattern in the Smalltalk Companion to the GOF book. On p. 339, they proposed the following "Smalltalk way" as an alternative to the common class-per-strategy implementation:
[[[language=smalltalk
Composition>>repair
"Without the strategy pattern, but using perform:."
| selector |
"Construct the name of the method to invoke:"
selector := ('formatWith', formattingStrategy, 'Algorithm') asSymbol.
self perform: selector
]]]
It then dismissed the approach as "''clever but difficult from a program understanding perspective. Even static analysis tools such as code browsers' "senders" and "messages" fail on this code.''"
It struck me as perhaps a bit extreme (i.e. too clever indeed) to construct the algorithm selector via string concatenation. Maybe "senders" search capabilities have gotten more sophisticated since publication, but Pharo seems to support symbol arguments, even for e.g. message renames. I thought, why not the following:
[[[language=smalltalk
Composition>>repair
"Without the strategy pattern, but using perform:."
self perform: self formattingStrategy
]]]
Then client code like ==aComposition formattingStrategy: #formatWithSimpleAlgorithm== would show up in senders, message renames, etc.
But from what youâre saying, I feel I may be missing somethingâ¦
-------------------------------------------- Stéphane Ducasse http://stephane.ducasse.free.fr / http://www.pharo.org 03 59 35 87 52 Assistant: Aurore Dalle FAX 03 59 57 78 50 TEL 03 59 35 86 16 S. Ducasse - Inria 40, avenue Halley, Parc Scientifique de la Haute Borne, Bât.A, Park Plaza Villeneuve d'Ascq 59650 France
Richard O'Keefe wrote
Whatever else it is, OOP is a means to an end, not an end in itself. It's not a religion.
Richard makes an important point here. As I mentioned on Discord (slightly edited to fit this thread), itâs a judgment call with trade-offs, but for the purposes of an OOP exercise, I would say absolutely put the methods in object and wherever else you may need them - if only to get practice with that particular idiom. I needed to do a lot of that sort of thing - probably way *too* much, just to break my procedural thinking habits. Once I got it "in my bones" I became more pragmatic. While in theory, this may always be the âmostâ OOP way, in practice it can be confusing due to the limitations of our system organization and the fact that people will have to scroll through more methods on kernel objects (not to mention the extra dependencies Richard noted). That is the dogma, and I think is a fine answer for an OOP exercise, but IMHO in practice there are justifiable exceptions. The two major axes are understandability and adaptability. If in your domain there are only two choices and there can not logically be more, it may be easier to understand one method with a conditional that documents that domain fact, than it would be to dive down a polymorphism rabbit hole spread across the system. Of course, tooling is a big factor in understandability. In GT it may be trivial because you can open implementors in a plane right next to the code browser. Different toolsets themselves mean different trade offs. There are no one size fits all answers for all time. There are principles that have to be negotiated with your current environment, use case, experience level, team size... ----- Cheers, Sean -- Sent from: http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html
I take Sean's point. However, while I agree that practising using polymorphism instead of 'if' is a good idea, I don't think that *this* exercise is a good one for getting such practice. Roelof is going through the Pharo track of Exercism. This particular one is called 'flatten-array'. The one concession to "hey, this is Pharo!" in the description of the exercise is a veiled warning against using Pharo's #flattened/#flattenOn:, which (a) does not add anything to Object or UndefinedObject (just Collection>>flattened and Collection>>flattenOn:) (b) does not make a special case of nil (c) DOES make a special case of strings, treating them as atomic. Possibly the most challenging part for me in this exercise was trying to figure out "what does <list> mean for Smalltalk here?" In Pharo's existing #flattened, why does a String count as atomic but a Semphore is just another collection? This is a Lisp programming exercise from the early 1960s. It had unpleasant ambiguities back then and it has not got better since. If this were rewritten as "Make a Composite implementation of binary search trees with a class for empty trees, a class for non-empty ones, and perhaps a class for singleton ones. Implement #do:, traversing the elements in increasing order. Use this to implement #asOrderedCollection." then that *would* be a good exercise for using polymorphism instead of conditionals. BST () asOrderedCollection ^OrderedCollection new in: [:coll | self do: [:each | coll addLast: each]. coll] EmptyBST () do: aBlock "Nothing to do." NonemptyBST (less key greater) do: aBlock less do: aBlock. aBlock value: key. greater do: aBlock. On Tue, 15 Sep 2020 at 18:33, Sean P. DeNigris <sean@clipperadams.com> wrote:
Richard O'Keefe wrote
Whatever else it is, OOP is a means to an end, not an end in itself. It's not a religion.
Richard makes an important point here.
As I mentioned on Discord (slightly edited to fit this thread), itâs a judgment call with trade-offs, but for the purposes of an OOP exercise, I would say absolutely put the methods in object and wherever else you may need them - if only to get practice with that particular idiom. I needed to do a lot of that sort of thing - probably way *too* much, just to break my procedural thinking habits. Once I got it "in my bones" I became more pragmatic. While in theory, this may always be the âmostâ OOP way, in practice it can be confusing due to the limitations of our system organization and the fact that people will have to scroll through more methods on kernel objects (not to mention the extra dependencies Richard noted). That is the dogma, and I think is a fine answer for an OOP exercise, but IMHO in practice there are justifiable exceptions. The two major axes are understandability and adaptability. If in your domain there are only two choices and there can not logically be more, it may be easier to understand one method with a conditional that documents that domain fact, than it would be to dive down a polymorphism rabbit hole spread across the system. Of course, tooling is a big factor in understandability. In GT it may be trivial because you can open implementors in a plane right next to the code browser. Different toolsets themselves mean different trade offs. There are no one size fits all answers for all time. There are principles that have to be negotiated with your current environment, use case, experience level, team size...
----- Cheers, Sean -- Sent from: http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html
participants (7)
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Noury Bouraqadi -
Richard O'Keefe -
Richard Sargent -
Roelof Wobben -
Sean P. DeNigris -
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Stéphane Ducasse