Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

Yeah, me too, preferring the first version, which I've archived as a
masterpiece at
https://github.com/suntong/lang/blob/master/lang/Go/src/oo/Polymorphism-AnimalVF3.go
with the following notes:

The best way to implement *virtual function* so far, that satisfies the
following challenges:

- Consider the "func Output()" as a *very complicated* function that I only
  want to define once at the base level, not to duplicate into each sub
  classes, yet it need to access member functions from sub classes.

- Meanwhile I have a *huge list* of common variables that I defined in my
  "base class", and using simple pure function will cause almost every
  single variable to be undefined: https://play.golang.org/p/QjCtD9rGpa

On Thu, Nov 24, 2016 at 9:37 PM, xingtao zhao wrote:

> Or this implementation: https://play.golang.org/p/5GqspHDJnF
> But I prefer the previous version: https://play.golang.org/p/3_PDTCcJTi.
>
>
> On Thursday, November 24, 2016 at 6:21:24 PM UTC-8, xingtao zhao wrote:
>>
>> Hi Tong,
>>
>> Another implementation is https://play.golang.org/p/3_PDTCcJTi.
>> You could merge the interface Animal and ExtraFactsor together if this
>> extra behavior is not needed. It is listed there just for demonstration.
>>
>

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Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

Oh, I like that. This is much better than my "double-passing" version, and
so far the best. Thanks a lot!

On Thu, Nov 24, 2016 at 9:21 PM, xingtao zhao  wrote:

> Hi Tong,
>
> Another implementation is https://play.golang.org/p/3_PDTCcJTi.
> You could merge the interface Animal and ExtraFactsor together if this
> extra behavior is not needed. It is listed there just for demonstration.
>
> On Thursday, November 24, 2016 at 12:14:37 AM UTC-8, Nick Patavalis wrote:
>>
>> On Thu, Nov 24, 2016 at 10:00 AM, Haddock  wrote:
>> >
>> > This is merely resorting to a shared function. This does not really
>> > cover overwriting in the OO sense. The article I mentioned shows how
>> > to do this:
>> > http://objectscape.blogspot.de/2013/09/inner-pattern-to-mimi
>> c-method.html
>>
>> Not really! Tong Sun's Animal.Output() method (with a Speaker
>> argument) is pretty-much "isomorphic" with Plohmann's Mamal.ActInner()
>> method (with an Animal argument). Maybe it's not as clearly named, but
>> it is pretty-much the same approach.
>>
>> /npat
>>
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Re: [go-nuts] Thinking OO virtual function in Go

[xingtao zhao]

Or this implementation: https://play.golang.org/p/5GqspHDJnF
But I prefer the previous version: https://play.golang.org/p/3_PDTCcJTi.

On Thursday, November 24, 2016 at 6:21:24 PM UTC-8, xingtao zhao wrote:
>
> Hi Tong,
>
> Another implementation is https://play.golang.org/p/3_PDTCcJTi.
> You could merge the interface Animal and ExtraFactsor together if this 
> extra behavior is not needed. It is listed there just for demonstration.
>
> On Thursday, November 24, 2016 at 12:14:37 AM UTC-8, Nick Patavalis wrote:
>>
>> On Thu, Nov 24, 2016 at 10:00 AM, Haddock  wrote: 
>> > 
>> > This is merely resorting to a shared function. This does not really 
>> > cover overwriting in the OO sense. The article I mentioned shows how 
>> > to do this: 
>> > 
>> http://objectscape.blogspot.de/2013/09/inner-pattern-to-mimic-method.html 
>>
>> Not really! Tong Sun's Animal.Output() method (with a Speaker 
>> argument) is pretty-much "isomorphic" with Plohmann's Mamal.ActInner() 
>> method (with an Animal argument). Maybe it's not as clearly named, but 
>> it is pretty-much the same approach. 
>>
>> /npat 
>>
>

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Re: [go-nuts] Thinking OO virtual function in Go

[xingtao zhao]

Hi Tong,

Another implementation is https://play.golang.org/p/3_PDTCcJTi.
You could merge the interface Animal and ExtraFactsor together if this 
extra behavior is not needed. It is listed there just for demonstration.

On Thursday, November 24, 2016 at 12:14:37 AM UTC-8, Nick Patavalis wrote:
>
> On Thu, Nov 24, 2016 at 10:00 AM, Haddock  
> wrote: 
> > 
> > This is merely resorting to a shared function. This does not really 
> > cover overwriting in the OO sense. The article I mentioned shows how 
> > to do this: 
> > 
> http://objectscape.blogspot.de/2013/09/inner-pattern-to-mimic-method.html 
>
> Not really! Tong Sun's Animal.Output() method (with a Speaker 
> argument) is pretty-much "isomorphic" with Plohmann's Mamal.ActInner() 
> method (with an Animal argument). Maybe it's not as clearly named, but 
> it is pretty-much the same approach. 
>
> /npat 
>

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Re: [go-nuts] Thinking OO virtual function in Go

[Nick Patavalis]

On Thu, Nov 24, 2016 at 10:00 AM, Haddock  wrote:
>
> This is merely resorting to a shared function. This does not really
> cover overwriting in the OO sense. The article I mentioned shows how
> to do this:
> http://objectscape.blogspot.de/2013/09/inner-pattern-to-mimic-method.html

Not really! Tong Sun's Animal.Output() method (with a Speaker
argument) is pretty-much "isomorphic" with Plohmann's Mamal.ActInner()
method (with an Animal argument). Maybe it's not as clearly named, but
it is pretty-much the same approach.

/npat

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Re: [go-nuts] Thinking OO virtual function in Go

[Haddock]

> I think I finally found the easiest way to make virtual function works, 
> based on Nick Patavalis code and Tahir Hashmi's idea:
>
>
> func (a Animal) Output(s Speaker) {
> // Complicated stuff that must not be re-implemented
> fmt.Print("I am a ", s.IsA(),
> ". My name is ", a.Name,
> ", aged ", a.Age,
> ", it is ", a.IsMale,
> " I am male.\n ")
> s.Speak()
> }
>
>
>
> https://github.com/suntong/lang/blob/master/lang/Go/src/oo/Polymorphism-AnimalVF2.go
>
>
This is merely resorting to a shared function. This does not really cover 
overwriting in the OO sense. The article I mentioned shows how to do this: 
http://objectscape.blogspot.de/2013/09/inner-pattern-to-mimic-method.html 


Cheers, Haddock
 

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Re: [go-nuts] Thinking OO virtual function in Go

[Nick Patavalis]

​
As I said
​ ​
before, Go's flavor of OO is different from that of other languages. Don't
try to map concepts one-to-one, or you will end up with very contrived
solutions. Always look at the big picture (why am I doing this?) and don't
get side-tracked by synthetic examples.

Most important is defining the correct interfaces (how your objects should
behave, what services they should provide); implementation reuse is
secondary. You will always find more than one ways to avoid repeating the
same code, on a per-case basis and you can always improve on that down the
way, provided that your interfaces are correct.

Just my 2c
/npat

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Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

On Wed, Nov 23, 2016 at 3:49 PM, Tong Sun wrote:

>
> On Wed, Nov 23, 2016 at 12:09 PM, Nick Patavalis wrote:
>
>> For this specific example, something like this:
>> https://play.golang.org/p/FsorWRaLKk
>>
>
> Thanks a lot Nick!
>
> I've simplified it a bit. Now it is:
>
> func (d Dog) Output() {
> // Presumably complicated stuff, not re-implemented
> d.Animal.Output(d.IsA())
> }
>
> I'm wondering if it is possible to somehow pass d.Speak as a function
> pointer to Animal.Output, so that inside Animal.Output, calling it will get
> to the correct dog.Speak or cat.Speak? Here is the code to start from:
>
> https://play.golang.org/p/cCmum-YRX9
>
> Thanks
>

I think I finally found the easiest way to make virtual function works,
based on Nick Patavalis code and Tahir Hashmi's idea:


func (a Animal) Output(s Speaker) {
// Complicated stuff that must not be re-implemented
fmt.Print("I am a ", s.IsA(),
". My name is ", a.Name,
", aged ", a.Age,
", it is ", a.IsMale,
" I am male.\n ")
s.Speak()
}


https://github.com/suntong/lang/blob/master/lang/Go/src/oo/Polymorphism-AnimalVF2.go

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Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

On Wed, Nov 23, 2016 at 12:09 PM, Nick Patavalis wrote:

> For this specific example, something like this: https://play.golang.org/p/
> FsorWRaLKk
>

Thanks a lot Nick!

I've simplified it a bit. Now it is:

func (d Dog) Output() {
// Presumably complicated stuff, not re-implemented
d.Animal.Output(d.IsA())
}

I'm wondering if it is possible to somehow pass d.Speak as a function
pointer to Animal.Output, so that inside Animal.Output, calling it will get
to the correct dog.Speak or cat.Speak? Here is the code to start from:

https://play.golang.org/p/cCmum-YRX9

Thanks

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Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

Thanks Chad. This is beyond my understanding for the moment, but I'm sure
it'd be handy someday... Thanks.

On Wed, Nov 23, 2016 at 1:17 PM,  wrote:

> Sorry, didn't read the whole thread, but here's how I tackled inheritance
> in my cross compiler: https://play.golang.org/p/UDp7nSLyl2. Granted, I am
> unsure about the unsafe thing, but the concept of a "method dispatcher" is
> likely what you need.
>
>
> On Wednesday, November 23, 2016 at 11:09:03 AM UTC-6, Nick Patavalis wrote:
>>
>>
>> On Wednesday, November 23, 2016 at 5:17:11 PM UTC+2, Tong Sun wrote:
>>>
>>> Can you make it work on play.golang.org, from this code
>>> https://play.golang.org/p/QjCtD9rGpa, according to your plan?
>>>
>>
>> For this specific example, something like this:
>> https://play.golang.org/p/FsorWRaLKk
>>
>> /npat
>>
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Re: [go-nuts] Thinking OO virtual function in Go

[chad . retz]

Sorry, didn't read the whole thread, but here's how I tackled inheritance 
in my cross compiler: https://play.golang.org/p/UDp7nSLyl2. Granted, I am 
unsure about the unsafe thing, but the concept of a "method dispatcher" is 
likely what you need.

On Wednesday, November 23, 2016 at 11:09:03 AM UTC-6, Nick Patavalis wrote:
>
>
> On Wednesday, November 23, 2016 at 5:17:11 PM UTC+2, Tong Sun wrote:
>>
>> Can you make it work on play.golang.org, from this code 
>> https://play.golang.org/p/QjCtD9rGpa, according to your plan?
>>
>
> For this specific example, something like this: 
> https://play.golang.org/p/FsorWRaLKk
>
> /npat
>
>

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Re: [go-nuts] Thinking OO virtual function in Go

[Nick Patavalis]

On Wednesday, November 23, 2016 at 5:17:11 PM UTC+2, Tong Sun wrote:
>
> Can you make it work on play.golang.org, from this code 
> https://play.golang.org/p/QjCtD9rGpa, according to your plan?
>

For this specific example, something like this: 
https://play.golang.org/p/FsorWRaLKk

/npat

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Re: [go-nuts] Thinking OO virtual function in Go

[Nick Patavalis]

Yes... so every specific animal type implements it's own Output() method,
which does the trivial IsA() part, and calls Animal's Output() for the
common complicated parts...

On Nov 23, 2016 16:35, "Tong Sun"  wrote:

> Have you noticed the IsA() func call there?
>
> On Wed, Nov 23, 2016 at 4:05 AM, Nick Patavalis 
> wrote:
>
>> Hi,
>>
>> In your *second* example, making Output() a method of Animal will work,
>> since it uses only the members (fields) of Animal, and not the fields of
>> specific animals (or any behavior that varies between animals). That's why
>> I'm insisting on *real* and *specific* examples, not synthetic ones.
>>
>> /npat
>>
>> On Wednesday, November 23, 2016 at 6:08:00 AM UTC+2, Tong Sun wrote:
>>>
>>> No Nick, making Output() a member method won't work.
>>> See my OP and Jesse's answer. I.e., I have to change it from a member
>>> function to a pure function.
>>>
>>> On Tue, Nov 22, 2016 at 6:25 PM, Nick Patavalis 
>>> wrote:
>>>
 Hi,

 There is no direct mapping of what you can do with virtual functions in
 other OO languages, and Go. There are different compromises you have to
 make; because of this, synthetic examples will probably not help much.

 That being said, in the case of your last example I would make Output()
 a method of Animal.
 The Speak() methods of the specific animals would then call Output().

 /npat

 On Wednesday, November 23, 2016 at 12:03:54 AM UTC+2, Tong Sun wrote:
>
>
>
> On Tue, Nov 22, 2016 at 4:29 PM, Jesse McNelis wrote:
>
>> On Wed, Nov 23, 2016 at 8:16 AM, Tong Sun wrote:
>> > Hi,
>> >
>> > How to architect the OO's virtual function in Go?
>> >
>> > Please take a look at this (not working) Go program
>> > https://play.golang.org/p/qrBX6ScABp
>> >
>> > Please think of the "func Output()" as a very complicated function
>> that I
>> > only want to define once at the base level, not to duplicate into
>> each sub
>> > classes.
>> >
>> > How can I make it works so that the last output statement, instead
>> of being,
>> >
>> > fmt.Printf("[%v] %s: [%0.2f]\n", k, v.Name(), v.Area())
>> >
>> >
>> > will be this instead:
>> >
>> > fmt.Printf("[%v] %s\n", k, v.Output())
>> >
>>
>> You define a function:
>>
>> func Output(s Shape) string {
>>return s.Name() + "'s area size is " + s.Area()
>> }
>>
>> Go uses interfaces for polymorphism.
>> Other OOP languages can use inheritance for polymorphism too, but Go
>> doesn't have inheritance.
>>
>
> Thanks Jesse. That works.
>
> However I just realized that it is only part of my problem.
>
> I have a huge list of common variables that I defined in my "base
> class", changing it from a member function to a pure function causes 
> almost
> every single variable now undefined.
>
> I can demonstrate the problem with this code
> https://play.golang.org/p/QjCtD9rGpa
>
> So, once again, thinking in OO, I'll define all of the common
> variables in base class, and common functionalities in virtual functions.
> How to make that idea work in Go?
>
> For the above specific code, how to easily make "func Output" works?
>
> Thanks
>
> --
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>>>
>>> --
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Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

Oh, I think you might not have notice this request from OP:

Please think of the "func Output()" as a very complicated function that I
> only want to define *once *at the base level, not to duplicate into each
> sub classes.



On Wed, Nov 23, 2016 at 10:16 AM, Tong Sun  wrote:

> Can you make it work on play.golang.org, from this code
> https://play.golang.org/p/QjCtD9rGpa, according to your plan?
>
> On Wed, Nov 23, 2016 at 10:14 AM, Nick Patavalis  > wrote:
>
>> Yes... so every specific animal type implements it's own Output() method,
>> which does the trivial IsA() part, and calls Animal's Output() for the
>> common complicated parts...
>>
>> On Nov 23, 2016 16:35, "Tong Sun"  wrote:
>>
>>> Have you noticed the IsA() func call there?
>>>
>>> On Wed, Nov 23, 2016 at 4:05 AM, Nick Patavalis <
>>> nick.patava...@gmail.com> wrote:
>>>
 Hi,

 In your *second* example, making Output() a method of Animal will work,
 since it uses only the members (fields) of Animal, and not the fields of
 specific animals (or any behavior that varies between animals). That's why
 I'm insisting on *real* and *specific* examples, not synthetic ones.

 /npat

 On Wednesday, November 23, 2016 at 6:08:00 AM UTC+2, Tong Sun wrote:
>
> No Nick, making Output() a member method won't work.
> See my OP and Jesse's answer. I.e., I have to change it from a member
> function to a pure function.
>
> On Tue, Nov 22, 2016 at 6:25 PM, Nick Patavalis 
> wrote:
>
>> Hi,
>>
>> There is no direct mapping of what you can do with virtual functions
>> in other OO languages, and Go. There are different compromises you have 
>> to
>> make; because of this, synthetic examples will probably not help much.
>>
>> That being said, in the case of your last example I would make
>> Output() a method of Animal.
>> The Speak() methods of the specific animals would then call Output().
>>
>> /npat
>>
>> On Wednesday, November 23, 2016 at 12:03:54 AM UTC+2, Tong Sun wrote:
>>>
>>>
>>>
>>> On Tue, Nov 22, 2016 at 4:29 PM, Jesse McNelis wrote:
>>>
 On Wed, Nov 23, 2016 at 8:16 AM, Tong Sun wrote:
 > Hi,
 >
 > How to architect the OO's virtual function in Go?
 >
 > Please take a look at this (not working) Go program
 > https://play.golang.org/p/qrBX6ScABp
 >
 > Please think of the "func Output()" as a very complicated
 function that I
 > only want to define once at the base level, not to duplicate into
 each sub
 > classes.
 >
 > How can I make it works so that the last output statement,
 instead of being,
 >
 > fmt.Printf("[%v] %s: [%0.2f]\n", k, v.Name(), v.Area())
 >
 >
 > will be this instead:
 >
 > fmt.Printf("[%v] %s\n", k, v.Output())
 >

 You define a function:

 func Output(s Shape) string {
return s.Name() + "'s area size is " + s.Area()
 }

 Go uses interfaces for polymorphism.
 Other OOP languages can use inheritance for polymorphism too, but Go
 doesn't have inheritance.

>>>
>>> Thanks Jesse. That works.
>>>
>>> However I just realized that it is only part of my problem.
>>>
>>> I have a huge list of common variables that I defined in my "base
>>> class", changing it from a member function to a pure function causes 
>>> almost
>>> every single variable now undefined.
>>>
>>> I can demonstrate the problem with this code
>>> https://play.golang.org/p/QjCtD9rGpa
>>>
>>> So, once again, thinking in OO, I'll define all of the common
>>> variables in base class, and common functionalities in virtual 
>>> functions.
>>> How to make that idea work in Go?
>>>
>>> For the above specific code, how to easily make "func Output" works?
>>>
>>> Thanks
>>>
>>> --
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Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

Can you make it work on play.golang.org, from this code
https://play.golang.org/p/QjCtD9rGpa, according to your plan?

On Wed, Nov 23, 2016 at 10:14 AM, Nick Patavalis 
wrote:

> Yes... so every specific animal type implements it's own Output() method,
> which does the trivial IsA() part, and calls Animal's Output() for the
> common complicated parts...
>
> On Nov 23, 2016 16:35, "Tong Sun"  wrote:
>
>> Have you noticed the IsA() func call there?
>>
>> On Wed, Nov 23, 2016 at 4:05 AM, Nick Patavalis > > wrote:
>>
>>> Hi,
>>>
>>> In your *second* example, making Output() a method of Animal will work,
>>> since it uses only the members (fields) of Animal, and not the fields of
>>> specific animals (or any behavior that varies between animals). That's why
>>> I'm insisting on *real* and *specific* examples, not synthetic ones.
>>>
>>> /npat
>>>
>>> On Wednesday, November 23, 2016 at 6:08:00 AM UTC+2, Tong Sun wrote:

 No Nick, making Output() a member method won't work.
 See my OP and Jesse's answer. I.e., I have to change it from a member
 function to a pure function.

 On Tue, Nov 22, 2016 at 6:25 PM, Nick Patavalis 
 wrote:

> Hi,
>
> There is no direct mapping of what you can do with virtual functions
> in other OO languages, and Go. There are different compromises you have to
> make; because of this, synthetic examples will probably not help much.
>
> That being said, in the case of your last example I would make
> Output() a method of Animal.
> The Speak() methods of the specific animals would then call Output().
>
> /npat
>
> On Wednesday, November 23, 2016 at 12:03:54 AM UTC+2, Tong Sun wrote:
>>
>>
>>
>> On Tue, Nov 22, 2016 at 4:29 PM, Jesse McNelis wrote:
>>
>>> On Wed, Nov 23, 2016 at 8:16 AM, Tong Sun wrote:
>>> > Hi,
>>> >
>>> > How to architect the OO's virtual function in Go?
>>> >
>>> > Please take a look at this (not working) Go program
>>> > https://play.golang.org/p/qrBX6ScABp
>>> >
>>> > Please think of the "func Output()" as a very complicated function
>>> that I
>>> > only want to define once at the base level, not to duplicate into
>>> each sub
>>> > classes.
>>> >
>>> > How can I make it works so that the last output statement, instead
>>> of being,
>>> >
>>> > fmt.Printf("[%v] %s: [%0.2f]\n", k, v.Name(), v.Area())
>>> >
>>> >
>>> > will be this instead:
>>> >
>>> > fmt.Printf("[%v] %s\n", k, v.Output())
>>> >
>>>
>>> You define a function:
>>>
>>> func Output(s Shape) string {
>>>return s.Name() + "'s area size is " + s.Area()
>>> }
>>>
>>> Go uses interfaces for polymorphism.
>>> Other OOP languages can use inheritance for polymorphism too, but Go
>>> doesn't have inheritance.
>>>
>>
>> Thanks Jesse. That works.
>>
>> However I just realized that it is only part of my problem.
>>
>> I have a huge list of common variables that I defined in my "base
>> class", changing it from a member function to a pure function causes 
>> almost
>> every single variable now undefined.
>>
>> I can demonstrate the problem with this code
>> https://play.golang.org/p/QjCtD9rGpa
>>
>> So, once again, thinking in OO, I'll define all of the common
>> variables in base class, and common functionalities in virtual functions.
>> How to make that idea work in Go?
>>
>> For the above specific code, how to easily make "func Output" works?
>>
>> Thanks
>>
>> --
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Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

Have you noticed the IsA() func call there?

On Wed, Nov 23, 2016 at 4:05 AM, Nick Patavalis 
wrote:

> Hi,
>
> In your *second* example, making Output() a method of Animal will work,
> since it uses only the members (fields) of Animal, and not the fields of
> specific animals (or any behavior that varies between animals). That's why
> I'm insisting on *real* and *specific* examples, not synthetic ones.
>
> /npat
>
> On Wednesday, November 23, 2016 at 6:08:00 AM UTC+2, Tong Sun wrote:
>>
>> No Nick, making Output() a member method won't work.
>> See my OP and Jesse's answer. I.e., I have to change it from a member
>> function to a pure function.
>>
>> On Tue, Nov 22, 2016 at 6:25 PM, Nick Patavalis 
>> wrote:
>>
>>> Hi,
>>>
>>> There is no direct mapping of what you can do with virtual functions in
>>> other OO languages, and Go. There are different compromises you have to
>>> make; because of this, synthetic examples will probably not help much.
>>>
>>> That being said, in the case of your last example I would make Output()
>>> a method of Animal.
>>> The Speak() methods of the specific animals would then call Output().
>>>
>>> /npat
>>>
>>> On Wednesday, November 23, 2016 at 12:03:54 AM UTC+2, Tong Sun wrote:



 On Tue, Nov 22, 2016 at 4:29 PM, Jesse McNelis wrote:

> On Wed, Nov 23, 2016 at 8:16 AM, Tong Sun wrote:
> > Hi,
> >
> > How to architect the OO's virtual function in Go?
> >
> > Please take a look at this (not working) Go program
> > https://play.golang.org/p/qrBX6ScABp
> >
> > Please think of the "func Output()" as a very complicated function
> that I
> > only want to define once at the base level, not to duplicate into
> each sub
> > classes.
> >
> > How can I make it works so that the last output statement, instead
> of being,
> >
> > fmt.Printf("[%v] %s: [%0.2f]\n", k, v.Name(), v.Area())
> >
> >
> > will be this instead:
> >
> > fmt.Printf("[%v] %s\n", k, v.Output())
> >
>
> You define a function:
>
> func Output(s Shape) string {
>return s.Name() + "'s area size is " + s.Area()
> }
>
> Go uses interfaces for polymorphism.
> Other OOP languages can use inheritance for polymorphism too, but Go
> doesn't have inheritance.
>

 Thanks Jesse. That works.

 However I just realized that it is only part of my problem.

 I have a huge list of common variables that I defined in my "base
 class", changing it from a member function to a pure function causes almost
 every single variable now undefined.

 I can demonstrate the problem with this code
 https://play.golang.org/p/QjCtD9rGpa

 So, once again, thinking in OO, I'll define all of the common variables
 in base class, and common functionalities in virtual functions. How to make
 that idea work in Go?

 For the above specific code, how to easily make "func Output" works?

 Thanks

 --
>>> You received this message because you are subscribed to a topic in the
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>>
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Re: [go-nuts] Thinking OO virtual function in Go

[Nick Patavalis]

Hi,

In your *second* example, making Output() a method of Animal will work, 
since it uses only the members (fields) of Animal, and not the fields of 
specific animals (or any behavior that varies between animals). That's why 
I'm insisting on *real* and *specific* examples, not synthetic ones.

/npat

On Wednesday, November 23, 2016 at 6:08:00 AM UTC+2, Tong Sun wrote:
>
> No Nick, making Output() a member method won't work. 
> See my OP and Jesse's answer. I.e., I have to change it from a member 
> function to a pure function. 
>
> On Tue, Nov 22, 2016 at 6:25 PM, Nick Patavalis  > wrote:
>
>> Hi,
>>
>> There is no direct mapping of what you can do with virtual functions in 
>> other OO languages, and Go. There are different compromises you have to 
>> make; because of this, synthetic examples will probably not help much. 
>>
>> That being said, in the case of your last example I would make Output() a 
>> method of Animal. 
>> The Speak() methods of the specific animals would then call Output().
>>
>> /npat
>>
>> On Wednesday, November 23, 2016 at 12:03:54 AM UTC+2, Tong Sun wrote:
>>>
>>>
>>>
>>> On Tue, Nov 22, 2016 at 4:29 PM, Jesse McNelis wrote:
>>>
 On Wed, Nov 23, 2016 at 8:16 AM, Tong Sun wrote:
 > Hi,
 >
 > How to architect the OO's virtual function in Go?
 >
 > Please take a look at this (not working) Go program
 > https://play.golang.org/p/qrBX6ScABp
 >
 > Please think of the "func Output()" as a very complicated function 
 that I
 > only want to define once at the base level, not to duplicate into 
 each sub
 > classes.
 >
 > How can I make it works so that the last output statement, instead of 
 being,
 >
 > fmt.Printf("[%v] %s: [%0.2f]\n", k, v.Name(), v.Area())
 >
 >
 > will be this instead:
 >
 > fmt.Printf("[%v] %s\n", k, v.Output())
 >

 You define a function:

 func Output(s Shape) string {
return s.Name() + "'s area size is " + s.Area()
 }

 Go uses interfaces for polymorphism.
 Other OOP languages can use inheritance for polymorphism too, but Go
 doesn't have inheritance.

>>>
>>> Thanks Jesse. That works. 
>>>
>>> However I just realized that it is only part of my problem. 
>>>
>>> I have a huge list of common variables that I defined in my "base 
>>> class", changing it from a member function to a pure function causes almost 
>>> every single variable now undefined. 
>>>
>>> I can demonstrate the problem with this code
>>> https://play.golang.org/p/QjCtD9rGpa
>>>
>>> So, once again, thinking in OO, I'll define all of the common variables 
>>> in base class, and common functionalities in virtual functions. How to make 
>>> that idea work in Go?
>>>
>>> For the above specific code, how to easily make "func Output" works?
>>>
>>> Thanks
>>>
>>> -- 
>> You received this message because you are subscribed to a topic in the 
>> Google Groups "golang-nuts" group.
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>
>

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Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

Thanks a lot for your explicit example. Much more helpful to me than merely
saying define getters. Much appreciate it!

On Tue, Nov 22, 2016 at 6:27 PM,  wrote:

> interfaces only work on methods.
>
> https://play.golang.org/p/o6Ot4IdJZ1
>
> Name, Age , ... are not methods they are fields.You need to make them part
> of Speaker interface by using methods instead of fields.
>
>
> Le mardi 22 novembre 2016 23:03:54 UTC+1, Tong Sun a écrit :
>>
>>
>>
>> On Tue, Nov 22, 2016 at 4:29 PM, Jesse McNelis wrote:
>>
>>> On Wed, Nov 23, 2016 at 8:16 AM, Tong Sun wrote:
>>> > Hi,
>>> >
>>> > How to architect the OO's virtual function in Go?
>>> >
>>> > Please take a look at this (not working) Go program
>>> > https://play.golang.org/p/qrBX6ScABp
>>> >
>>> > Please think of the "func Output()" as a very complicated function
>>> that I
>>> > only want to define once at the base level, not to duplicate into each
>>> sub
>>> > classes.
>>> >
>>> > How can I make it works so that the last output statement, instead of
>>> being,
>>> >
>>> > fmt.Printf("[%v] %s: [%0.2f]\n", k, v.Name(), v.Area())
>>> >
>>> >
>>> > will be this instead:
>>> >
>>> > fmt.Printf("[%v] %s\n", k, v.Output())
>>> >
>>>
>>> You define a function:
>>>
>>> func Output(s Shape) string {
>>>return s.Name() + "'s area size is " + s.Area()
>>> }
>>>
>>> Go uses interfaces for polymorphism.
>>> Other OOP languages can use inheritance for polymorphism too, but Go
>>> doesn't have inheritance.
>>>
>>
>> Thanks Jesse. That works.
>>
>> However I just realized that it is only part of my problem.
>>
>> I have a huge list of common variables that I defined in my "base class",
>> changing it from a member function to a pure function causes almost every
>> single variable now undefined.
>>
>> I can demonstrate the problem with this code
>> https://play.golang.org/p/QjCtD9rGpa
>>
>> So, once again, thinking in OO, I'll define all of the common variables
>> in base class, and common functionalities in virtual functions. How to make
>> that idea work in Go?
>>
>> For the above specific code, how to easily make "func Output" works?
>>
>> Thanks
>>
>> --
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Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

No Nick, making Output() a member method won't work.
See my OP and Jesse's answer. I.e., I have to change it from a member
function to a pure function.

On Tue, Nov 22, 2016 at 6:25 PM, Nick Patavalis 
wrote:

> Hi,
>
> There is no direct mapping of what you can do with virtual functions in
> other OO languages, and Go. There are different compromises you have to
> make; because of this, synthetic examples will probably not help much.
>
> That being said, in the case of your last example I would make Output() a
> method of Animal.
> The Speak() methods of the specific animals would then call Output().
>
> /npat
>
> On Wednesday, November 23, 2016 at 12:03:54 AM UTC+2, Tong Sun wrote:
>>
>>
>>
>> On Tue, Nov 22, 2016 at 4:29 PM, Jesse McNelis wrote:
>>
>>> On Wed, Nov 23, 2016 at 8:16 AM, Tong Sun wrote:
>>> > Hi,
>>> >
>>> > How to architect the OO's virtual function in Go?
>>> >
>>> > Please take a look at this (not working) Go program
>>> > https://play.golang.org/p/qrBX6ScABp
>>> >
>>> > Please think of the "func Output()" as a very complicated function
>>> that I
>>> > only want to define once at the base level, not to duplicate into each
>>> sub
>>> > classes.
>>> >
>>> > How can I make it works so that the last output statement, instead of
>>> being,
>>> >
>>> > fmt.Printf("[%v] %s: [%0.2f]\n", k, v.Name(), v.Area())
>>> >
>>> >
>>> > will be this instead:
>>> >
>>> > fmt.Printf("[%v] %s\n", k, v.Output())
>>> >
>>>
>>> You define a function:
>>>
>>> func Output(s Shape) string {
>>>return s.Name() + "'s area size is " + s.Area()
>>> }
>>>
>>> Go uses interfaces for polymorphism.
>>> Other OOP languages can use inheritance for polymorphism too, but Go
>>> doesn't have inheritance.
>>>
>>
>> Thanks Jesse. That works.
>>
>> However I just realized that it is only part of my problem.
>>
>> I have a huge list of common variables that I defined in my "base class",
>> changing it from a member function to a pure function causes almost every
>> single variable now undefined.
>>
>> I can demonstrate the problem with this code
>> https://play.golang.org/p/QjCtD9rGpa
>>
>> So, once again, thinking in OO, I'll define all of the common variables
>> in base class, and common functionalities in virtual functions. How to make
>> that idea work in Go?
>>
>> For the above specific code, how to easily make "func Output" works?
>>
>> Thanks
>>
>> --
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Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

On Tue, Nov 22, 2016 at 6:23 PM, Jesse McNelis wrote:

> On 23 Nov. 2016 9:03 am, "Tong Sun" wrote:
> >
> > So, once again, thinking in OO, I'll define all of the common variables
> in base class, and common functionalities in virtual functions. How to make
> that idea work in Go?
> >
> > For the above specific code, how to easily make "func Output" works?
> >
>
> You can use functions and embedding for code reuse and interfaces for
> polymorphism.
>
> In your example you've implemented Speak() method for each type and
> defined a Speaker interface but then in Output() you don't call Speak().
>
Yeah, that Output() is the virtual function I'm implementing. In my real
code it has nothing to do with Speak() method, only to use those common
variables.

> If you have fields you want available through the Speaker interface then
> you need to define getter methods for those fields and add them to the
> interface.
>
Got it.

> You could also add a Speak() method to the Animal type which would then be
> available on any type that embeds an Animal and would have direct access to
> any fields on Animal.
>
However, different animals speak differently. I.e., it is not the fields on
Animal that matter but what outside it matter to Speak(), right? So adding
a Speak() method to the Animal doesn't make much sense, right?


> You could define a Speak() function that all the Speak() methods call for
> some common functionality.
>
> How you structure it depends on what real world problem you're trying to
> solve.
>
Probably, but just thinking in abstract terms, I thought there are some
basic principles that people can follow. Anyway, I think paraiso.marc's
methodology might be the only way.

>

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Re: [go-nuts] Thinking OO virtual function in Go

[paraiso . marc]

interfaces only work on methods. 

https://play.golang.org/p/o6Ot4IdJZ1

Name, Age , ... are not methods they are fields.You need to make them part 
of Speaker interface by using methods instead of fields.

Le mardi 22 novembre 2016 23:03:54 UTC+1, Tong Sun a écrit :
>
>
>
> On Tue, Nov 22, 2016 at 4:29 PM, Jesse McNelis wrote:
>
>> On Wed, Nov 23, 2016 at 8:16 AM, Tong Sun wrote:
>> > Hi,
>> >
>> > How to architect the OO's virtual function in Go?
>> >
>> > Please take a look at this (not working) Go program
>> > https://play.golang.org/p/qrBX6ScABp
>> >
>> > Please think of the "func Output()" as a very complicated function that 
>> I
>> > only want to define once at the base level, not to duplicate into each 
>> sub
>> > classes.
>> >
>> > How can I make it works so that the last output statement, instead of 
>> being,
>> >
>> > fmt.Printf("[%v] %s: [%0.2f]\n", k, v.Name(), v.Area())
>> >
>> >
>> > will be this instead:
>> >
>> > fmt.Printf("[%v] %s\n", k, v.Output())
>> >
>>
>> You define a function:
>>
>> func Output(s Shape) string {
>>return s.Name() + "'s area size is " + s.Area()
>> }
>>
>> Go uses interfaces for polymorphism.
>> Other OOP languages can use inheritance for polymorphism too, but Go
>> doesn't have inheritance.
>>
>
> Thanks Jesse. That works. 
>
> However I just realized that it is only part of my problem. 
>
> I have a huge list of common variables that I defined in my "base class", 
> changing it from a member function to a pure function causes almost every 
> single variable now undefined. 
>
> I can demonstrate the problem with this code
> https://play.golang.org/p/QjCtD9rGpa
>
> So, once again, thinking in OO, I'll define all of the common variables in 
> base class, and common functionalities in virtual functions. How to make 
> that idea work in Go?
>
> For the above specific code, how to easily make "func Output" works?
>
> Thanks
>
>

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Re: [go-nuts] Thinking OO virtual function in Go

[Jesse McNelis]

On 23 Nov. 2016 9:03 am, "Tong Sun"  wrote:
>
> So, once again, thinking in OO, I'll define all of the common variables
in base class, and common functionalities in virtual functions. How to make
that idea work in Go?
>
> For the above specific code, how to easily make "func Output" works?
>

You can use functions and embedding for code reuse and interfaces for
polymorphism.

In your example you've implemented Speak() method for each type and defined
a Speaker interface but then in Output() you don't call Speak().

If you have fields you want available through the Speaker interface then
you need to define getter methods for those fields and add them to the
interface.

You could also add a Speak() method to the Animal type which would then be
available on any type that embeds an Animal and would have direct access to
any fields on Animal.

You could define a Speak() function that all the Speak() methods call for
some common functionality.

How you structure it depends on what real world problem you're trying to
solve.

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Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

On Tue, Nov 22, 2016 at 4:29 PM, Jesse McNelis wrote:

> On Wed, Nov 23, 2016 at 8:16 AM, Tong Sun wrote:
> > Hi,
> >
> > How to architect the OO's virtual function in Go?
> >
> > Please take a look at this (not working) Go program
> > https://play.golang.org/p/qrBX6ScABp
> >
> > Please think of the "func Output()" as a very complicated function that I
> > only want to define once at the base level, not to duplicate into each
> sub
> > classes.
> >
> > How can I make it works so that the last output statement, instead of
> being,
> >
> > fmt.Printf("[%v] %s: [%0.2f]\n", k, v.Name(), v.Area())
> >
> >
> > will be this instead:
> >
> > fmt.Printf("[%v] %s\n", k, v.Output())
> >
>
> You define a function:
>
> func Output(s Shape) string {
>return s.Name() + "'s area size is " + s.Area()
> }
>
> Go uses interfaces for polymorphism.
> Other OOP languages can use inheritance for polymorphism too, but Go
> doesn't have inheritance.
>

Thanks Jesse. That works.

However I just realized that it is only part of my problem.

I have a huge list of common variables that I defined in my "base class",
changing it from a member function to a pure function causes almost every
single variable now undefined.

I can demonstrate the problem with this code
https://play.golang.org/p/QjCtD9rGpa

So, once again, thinking in OO, I'll define all of the common variables in
base class, and common functionalities in virtual functions. How to make
that idea work in Go?

For the above specific code, how to easily make "func Output" works?

Thanks

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Re: [go-nuts] Thinking OO virtual function in Go

[Tong Sun]

On Tue, Nov 22, 2016 at 4:29 PM, Seb Binet wrote:

>
>
> On Tue, Nov 22, 2016 at 10:16 PM, Tong Sun wrote:
>
>> Hi,
>>
>> How to architect the OO's virtual function in Go?
>>
>> Please take a look at this (not working) Go program
>> https://play.golang.org/p/qrBX6ScABp
>>
>> Please think of the "func Output()" as a very complicated function that I
>> only want to define *once *at the base level, not to duplicate into each
>> sub classes.
>>
>> How can I make it works so that the last output statement, instead of
>> being,
>>
>> fmt.Printf("[%v] %s: [%0.2f]\n", k, v.Name(), v.Area())
>>
>>
>> will be this instead:
>>
>> fmt.Printf("[%v] %s\n", k, v.Output())
>>
>>
> what about this:
>  https://play.golang.org/p/DdZBiOgF2w
>


Aha, that way. I've been banning my head for a while & you saved my day.
Thanks a lot!

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Re: [go-nuts] Thinking OO virtual function in Go

[Seb Binet]

On Tue, Nov 22, 2016 at 10:16 PM, Tong Sun  wrote:

> Hi,
>
> How to architect the OO's virtual function in Go?
>
> Please take a look at this (not working) Go program
> https://play.golang.org/p/qrBX6ScABp
>
> Please think of the "func Output()" as a very complicated function that I
> only want to define *once *at the base level, not to duplicate into each
> sub classes.
>
> How can I make it works so that the last output statement, instead of
> being,
>
> fmt.Printf("[%v] %s: [%0.2f]\n", k, v.Name(), v.Area())
>
>
> will be this instead:
>
> fmt.Printf("[%v] %s\n", k, v.Output())
>
>
what about this:
 https://play.golang.org/p/DdZBiOgF2w

-s

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Re: [go-nuts] Thinking OO virtual function in Go

[Jesse McNelis]

On Wed, Nov 23, 2016 at 8:16 AM, Tong Sun  wrote:
> Hi,
>
> How to architect the OO's virtual function in Go?
>
> Please take a look at this (not working) Go program
> https://play.golang.org/p/qrBX6ScABp
>
> Please think of the "func Output()" as a very complicated function that I
> only want to define once at the base level, not to duplicate into each sub
> classes.
>
> How can I make it works so that the last output statement, instead of being,
>
> fmt.Printf("[%v] %s: [%0.2f]\n", k, v.Name(), v.Area())
>
>
> will be this instead:
>
> fmt.Printf("[%v] %s\n", k, v.Output())
>

You define a function:

func Output(s Shape) string {
   return s.Name() + "'s area size is " + s.Area()
}

Go uses interfaces for polymorphism.
Other OOP languages can use inheritance for polymorphism too, but Go
doesn't have inheritance.

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