'Interface' Considered Harmful : Uncle Bob
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Hi, In his recent blog[^] Uncle Bob come up with a situation that explains
interfaceis harmful. Here is the code snippet taken from his blog.public class Subject {
private List<Observer> observers = new ArrayList<>();
private void register(Observer o) {
observers.add(o);
}
private void notify() {
for (Observer o : observers)
o.update();
}
}public class MyWidget {...}
public class MyObservableWidget extends MyWidget, Subject {
...
}Here he explains that to implement Observer pattern done correctly, compilers must allow multiple inheritance. So my question is why don't the
MyObservableWidgetimplement using dependency injection like below to avoid multiple inheritance with greater degree of separation of concerns?public class MyObservableWidget extends MyWidget {
private Subject subject;
public MyObservableWidget(Subject subject) {
this.subject = subject;
}}
Of course the
Subjectclass should be an abstract class. Please let me know your thoughts. Thanks, Pop -
Hi, In his recent blog[^] Uncle Bob come up with a situation that explains
interfaceis harmful. Here is the code snippet taken from his blog.public class Subject {
private List<Observer> observers = new ArrayList<>();
private void register(Observer o) {
observers.add(o);
}
private void notify() {
for (Observer o : observers)
o.update();
}
}public class MyWidget {...}
public class MyObservableWidget extends MyWidget, Subject {
...
}Here he explains that to implement Observer pattern done correctly, compilers must allow multiple inheritance. So my question is why don't the
MyObservableWidgetimplement using dependency injection like below to avoid multiple inheritance with greater degree of separation of concerns?public class MyObservableWidget extends MyWidget {
private Subject subject;
public MyObservableWidget(Subject subject) {
this.subject = subject;
}}
Of course the
Subjectclass should be an abstract class. Please let me know your thoughts. Thanks, Pop"Ivory tower theorizing considered harmful." -- DMR
-
"Ivory tower theorizing considered harmful." -- DMR
:-D
-
Hi, In his recent blog[^] Uncle Bob come up with a situation that explains
interfaceis harmful. Here is the code snippet taken from his blog.public class Subject {
private List<Observer> observers = new ArrayList<>();
private void register(Observer o) {
observers.add(o);
}
private void notify() {
for (Observer o : observers)
o.update();
}
}public class MyWidget {...}
public class MyObservableWidget extends MyWidget, Subject {
...
}Here he explains that to implement Observer pattern done correctly, compilers must allow multiple inheritance. So my question is why don't the
MyObservableWidgetimplement using dependency injection like below to avoid multiple inheritance with greater degree of separation of concerns?public class MyObservableWidget extends MyWidget {
private Subject subject;
public MyObservableWidget(Subject subject) {
this.subject = subject;
}}
Of course the
Subjectclass should be an abstract class. Please let me know your thoughts. Thanks, PopI gather that this article needed the help of a proctologist with a torch.
-
I gather that this article needed the help of a proctologist with a torch.
-
I gather that this article needed the help of a proctologist with a torch.
Was that a brainless question? :(
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Was that a brainless question? :(
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Oh that explains the hatred towards my question. But I was not trying to degrade that article. All I meant about the technical aspects of that idea. Sorry for my ignorance; I thought my solution can overcome the problem specified in the article. Thanks, Pop
-
Oh that explains the hatred towards my question. But I was not trying to degrade that article. All I meant about the technical aspects of that idea. Sorry for my ignorance; I thought my solution can overcome the problem specified in the article. Thanks, Pop
-
Thank you! :)
-
Oh that explains the hatred towards my question. But I was not trying to degrade that article. All I meant about the technical aspects of that idea. Sorry for my ignorance; I thought my solution can overcome the problem specified in the article. Thanks, Pop
Was there hatred towards your article? I was actually commenting that o' Uncle Bob seemed to have pulled his argument out of his posterior.
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Was there hatred towards your article? I was actually commenting that o' Uncle Bob seemed to have pulled his argument out of his posterior.
Sorry I was perplexed
-
Hi, In his recent blog[^] Uncle Bob come up with a situation that explains
interfaceis harmful. Here is the code snippet taken from his blog.public class Subject {
private List<Observer> observers = new ArrayList<>();
private void register(Observer o) {
observers.add(o);
}
private void notify() {
for (Observer o : observers)
o.update();
}
}public class MyWidget {...}
public class MyObservableWidget extends MyWidget, Subject {
...
}Here he explains that to implement Observer pattern done correctly, compilers must allow multiple inheritance. So my question is why don't the
MyObservableWidgetimplement using dependency injection like below to avoid multiple inheritance with greater degree of separation of concerns?public class MyObservableWidget extends MyWidget {
private Subject subject;
public MyObservableWidget(Subject subject) {
this.subject = subject;
}}
Of course the
Subjectclass should be an abstract class. Please let me know your thoughts. Thanks, PopHi, Thank you for the blog link. You propose what is called mixin, which is really the go to solution to avoid bloated inheritance hierarchies. The good thing about mixin of Subject is that you hide functionality and avoids to duplicate the code in Subject. The bad thing is that you still need to duplicate the code that calls Subject aka relaying. DI with mixin is also good since you make the dependency known to the outside. This opens up for implementation replacement from the outside and gives better transparency. However, Uncle Bob really wants to hide stuff and use inheritance to avoid ANY code duplication and he can't do that in a single inheritance language. I love interfaces because they form a specification layer without any implementation details. I love abstract classes because they can be implementation templates for concrete classes. I do not want to mix the 2 concerns - at all. And it IS a tad annoying when you need add mixin in you abstract classes to avoid code duplication. I wouldn't mind multiple inheritance, if the language/compiler could manage diamonds in a consistent and obvious way (No, C++ doesn't). The class hierarchy is however implementation - not specification (IMHO). Uncle Bob doesn't address that view on the interface keyword.... and I am not sure the interface keyword had that view in mind when invented.
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Hi, Thank you for the blog link. You propose what is called mixin, which is really the go to solution to avoid bloated inheritance hierarchies. The good thing about mixin of Subject is that you hide functionality and avoids to duplicate the code in Subject. The bad thing is that you still need to duplicate the code that calls Subject aka relaying. DI with mixin is also good since you make the dependency known to the outside. This opens up for implementation replacement from the outside and gives better transparency. However, Uncle Bob really wants to hide stuff and use inheritance to avoid ANY code duplication and he can't do that in a single inheritance language. I love interfaces because they form a specification layer without any implementation details. I love abstract classes because they can be implementation templates for concrete classes. I do not want to mix the 2 concerns - at all. And it IS a tad annoying when you need add mixin in you abstract classes to avoid code duplication. I wouldn't mind multiple inheritance, if the language/compiler could manage diamonds in a consistent and obvious way (No, C++ doesn't). The class hierarchy is however implementation - not specification (IMHO). Uncle Bob doesn't address that view on the interface keyword.... and I am not sure the interface keyword had that view in mind when invented.
Keld Ølykke wrote:
No, C++ doesn't
I think it does. Why do you say it doesn't?
Keld Ølykke wrote:
class hierarchy is however implementation - not specification
Agreed. Hence, I don't think interfaces are "harmful", but what Uncle Bob was really complaining about is not being able to have multiple base classes. However, I think true separation of concerns would use neither DI nor inheritance to do his observer pattern but rather a separate "observer manager" class that does both the observing and registration/deregistration.
#SupportHeForShe
If your actions inspire others to dream more, learn more, do more and become more, you are a leader.-John Q. Adams You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun Only 2 things are infinite, the universe and human stupidity, and I'm not sure about the former.-Albert Einstein
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Keld Ølykke wrote:
No, C++ doesn't
I think it does. Why do you say it doesn't?
Keld Ølykke wrote:
class hierarchy is however implementation - not specification
Agreed. Hence, I don't think interfaces are "harmful", but what Uncle Bob was really complaining about is not being able to have multiple base classes. However, I think true separation of concerns would use neither DI nor inheritance to do his observer pattern but rather a separate "observer manager" class that does both the observing and registration/deregistration.
#SupportHeForShe
If your actions inspire others to dream more, learn more, do more and become more, you are a leader.-John Q. Adams You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun Only 2 things are infinite, the universe and human stupidity, and I'm not sure about the former.-Albert Einstein
Well, by not consistent I mean that you can end up with compiler accepted code, but it is unknown what it will do. The "dreaded diamond" refers to the situation where class C inherits from 2 classes B1 & B2 that both inherits the same base A. C will have 2 copies of all fields from A and at runtime it is undefined which copy you address.
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Well, by not consistent I mean that you can end up with compiler accepted code, but it is unknown what it will do. The "dreaded diamond" refers to the situation where class C inherits from 2 classes B1 & B2 that both inherits the same base A. C will have 2 copies of all fields from A and at runtime it is undefined which copy you address.
Ah, sure, I see. But you can solve that by using "virtual" inheritance. Then there's only one instance of A. Of course, you can't always do that when using third-party libraries.
#SupportHeForShe
If your actions inspire others to dream more, learn more, do more and become more, you are a leader.-John Q. Adams You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun Only 2 things are infinite, the universe and human stupidity, and I'm not sure about the former.-Albert Einstein
-
Ah, sure, I see. But you can solve that by using "virtual" inheritance. Then there's only one instance of A. Of course, you can't always do that when using third-party libraries.
#SupportHeForShe
If your actions inspire others to dream more, learn more, do more and become more, you are a leader.-John Q. Adams You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun Only 2 things are infinite, the universe and human stupidity, and I'm not sure about the former.-Albert Einstein
Yes. If C++ was a game I would call it a tad unforgiving :-)
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Hi, In his recent blog[^] Uncle Bob come up with a situation that explains
interfaceis harmful. Here is the code snippet taken from his blog.public class Subject {
private List<Observer> observers = new ArrayList<>();
private void register(Observer o) {
observers.add(o);
}
private void notify() {
for (Observer o : observers)
o.update();
}
}public class MyWidget {...}
public class MyObservableWidget extends MyWidget, Subject {
...
}Here he explains that to implement Observer pattern done correctly, compilers must allow multiple inheritance. So my question is why don't the
MyObservableWidgetimplement using dependency injection like below to avoid multiple inheritance with greater degree of separation of concerns?public class MyObservableWidget extends MyWidget {
private Subject subject;
public MyObservableWidget(Subject subject) {
this.subject = subject;
}}
Of course the
Subjectclass should be an abstract class. Please let me know your thoughts. Thanks, Pop#강남풀싸롱신세경,#강남풀쌀롱,#강남풀싸롱
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