Interfaces

[Duncan McNutt .[FTSE]]

Why does code derive from for example, IComparer

ie,

class SomeClass : IComparer
{
public SomeClass()
{
}

public int Compare(object x, object y)
{
return someInt;
}
}


When it just uses that and could have done without deriving ICompare and
got the same result.

class SomeClass
{
public SomeClass()
{
}

public int Compare(object x, object y)
{
return someInt;
}
}

--

Duncan McNutt
Microsoft Product Deactivation Team
--

[Duncan McNutt .[FTSE]]

Re: Interfaces

And another question...

Because SomeClass derives from the IComparer interface


if i use SomeClass as a base of another like...

class SomeNewClass : SomeClass
{
public SomeNewClass()
{
}
}

Would that above fail due to no Compare method as SomeClass is derived from
ICompare and it MUST implement Compare.. like..

class SomeNewClass : SomeClass
{
public SomeNewClass()
{
}

public int Compare(object x, object y)
{
return someInt;
}
}

The above would work.

Do i understand this correctly?

--

Duncan McNutt
Microsoft Product Deactivation Team
--


" Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
news:uLBzK$kZDH A.2668@TK2MSFTN GP09.phx.gbl...[color=blue]
> Why does code derive from for example, IComparer
>
> ie,
>
> class SomeClass : IComparer
> {
> public SomeClass()
> {
> }
>
> public int Compare(object x, object y)
> {
> return someInt;
> }
> }
>
>
> When it just uses that and could have done without deriving ICompare[/color]
and[color=blue]
> got the same result.
>
> class SomeClass
> {
> public SomeClass()
> {
> }
>
> public int Compare(object x, object y)
> {
> return someInt;
> }
> }
>
> --
>
> Duncan McNutt
> Microsoft Product Deactivation Team
> --
>
>
>[/color]

[Ignacio Machin]

Re: Interfaces

Hi Duncan,

You do not derive from an interface, you implement it, there is a diference,
an interface is like a template, it has no implementation it only assure
that the classes that implement it have a predefined setof methods ( the
interface ) , when you derive from a class you extend that class, add new
functionality. you do not do that with an interface.

Hope this help,

--
Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation


" Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
news:uLBzK$kZDH A.2668@TK2MSFTN GP09.phx.gbl...[color=blue]
> Why does code derive from for example, IComparer
>
> ie,
>
> class SomeClass : IComparer
> {
> public SomeClass()
> {
> }
>
> public int Compare(object x, object y)
> {
> return someInt;
> }
> }
>
>
> When it just uses that and could have done without deriving ICompare[/color]
and[color=blue]
> got the same result.
>
> class SomeClass
> {
> public SomeClass()
> {
> }
>
> public int Compare(object x, object y)
> {
> return someInt;
> }
> }
>
> --
>
> Duncan McNutt
> Microsoft Product Deactivation Team
> --
>
>
>[/color]

[Duncan McNutt .[FTSE]]

Re: Interfaces

oh well yeah oops :D wasnt thinking *gets coffee*

So why inherit from ICompare when its just as easy to implement Compare
anyway and its derived.

--

Duncan McNutt
Microsoft Product Deactivation Team
--


"Peter Vidler" <pvidler@gawab. com> wrote in message
news:bjp0b.27$g c6.35789@newsfe p1-win.server.ntli .net...[color=blue]
> Hi,
>[color=green]
> > Would that above fail due to no Compare method as SomeClass is
> > derived from ICompare and it MUST implement Compare.. like..[/color]
>
> No, because SomeNewClass will inherit the implementation from SomeClass.[/color]
I'm[color=blue]
> almost certain of it ;)
>
> Pete
>
>[/color]

[Duncan McNutt .[FTSE]]

Re: Interfaces

Yeah I understand an Interface is a contract, that must be implemented but I
see code that has implemented that interface but why would it need to when
it can just as easily implement it anyway and not have tim use ICompare in
the class definition.

Whats to stop me just coding a public int Compare(object x, object y) method
anyway without referring to IComapre?



--

Duncan McNutt
Microsoft Product Deactivation Team
--


"Ignacio Machin" <ignacio.mach in AT dot.state.fl.us > wrote in message
news:uL48cNlZDH A.3768@tk2msftn gp13.phx.gbl...[color=blue]
> Hi Duncan,
>
> You do not derive from an interface, you implement it, there is a[/color]
diference,[color=blue]
> an interface is like a template, it has no implementation it only assure
> that the classes that implement it have a predefined setof methods ( the
> interface ) , when you derive from a class you extend that class, add new
> functionality. you do not do that with an interface.
>
> Hope this help,
>
> --
> Ignacio Machin,
> ignacio.machin AT dot.state.fl.us
> Florida Department Of Transportation
>
>
> " Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
> news:uLBzK$kZDH A.2668@TK2MSFTN GP09.phx.gbl...[color=green]
> > Why does code derive from for example, IComparer
> >
> > ie,
> >
> > class SomeClass : IComparer
> > {
> > public SomeClass()
> > {
> > }
> >
> > public int Compare(object x, object y)
> > {
> > return someInt;
> > }
> > }
> >
> >
> > When it just uses that and could have done without deriving ICompare[/color]
> and[color=green]
> > got the same result.
> >
> > class SomeClass
> > {
> > public SomeClass()
> > {
> > }
> >
> > public int Compare(object x, object y)
> > {
> > return someInt;
> > }
> > }
> >
> > --
> >
> > Duncan McNutt
> > Microsoft Product Deactivation Team
> > --
> >
> >
> >[/color]
>
>[/color]

[Ignacio Machin]

Re: Interfaces

Hi Duncan,


I would suggest you something, if you have this kind of doubt, try it !! ,
do not missunderstand me, I believe that the best way to learn is
experimenting, your code will not fail cause as I explained in the previous
post when you derive you are extending therefore the new class gets all the
parent's functionality.

Hope this help,

--
Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation


" Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
news:ekcmmBlZDH A.1940@TK2MSFTN GP10.phx.gbl...[color=blue]
> And another question...
>
> Because SomeClass derives from the IComparer interface
>
>
> if i use SomeClass as a base of another like...
>
> class SomeNewClass : SomeClass
> {
> public SomeNewClass()
> {
> }
> }
>
> Would that above fail due to no Compare method as SomeClass is derived[/color]
from[color=blue]
> ICompare and it MUST implement Compare.. like..
>
> class SomeNewClass : SomeClass
> {
> public SomeNewClass()
> {
> }
>
> public int Compare(object x, object y)
> {
> return someInt;
> }
> }
>
> The above would work.
>
> Do i understand this correctly?
>
> --
>
> Duncan McNutt
> Microsoft Product Deactivation Team
> --
>
>
> " Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
> news:uLBzK$kZDH A.2668@TK2MSFTN GP09.phx.gbl...[color=green]
> > Why does code derive from for example, IComparer
> >
> > ie,
> >
> > class SomeClass : IComparer
> > {
> > public SomeClass()
> > {
> > }
> >
> > public int Compare(object x, object y)
> > {
> > return someInt;
> > }
> > }
> >
> >
> > When it just uses that and could have done without deriving ICompare[/color]
> and[color=green]
> > got the same result.
> >
> > class SomeClass
> > {
> > public SomeClass()
> > {
> > }
> >
> > public int Compare(object x, object y)
> > {
> > return someInt;
> > }
> > }
> >
> > --
> >
> > Duncan McNutt
> > Microsoft Product Deactivation Team
> > --
> >
> >
> >[/color]
>
>[/color]

[Peter Vidler]

Re: Interfaces

Hi,
[color=blue]
> So why inherit from ICompare when its just as easy to implement
> Compare anyway and its derived.[/color]

Because then you can use an object of that type wherever IComparer is asked
for (i.e. calls to methods, etc). Otherwise there is no way to tell if an
object supports the Compare method without having a reference to the exact
type of the object.

Pete

[Frank Drebin]

Re: Interfaces

The key element is that the purpose of an interface is that you can write
your code to a generic "interface" ..

For example, say you have a Windows app that needs to connect to a
datasource. That datasource could be a real database, a remote web service
and also an offline file. But you want to abstract HOW the datasource gets
it's data. If you couldn't abstract it, you'd have to write 3 versions of
code mixed in with your main application - to do this.

but instead, you could write your application to use the IDataAccess
interface (this is an interface you write, it has Connect() Authenticate(),
etc)..

Then you have classes such as Database, WebService and OfflineAccess that
implement that interface.

So Interfaces aren't so much a small-scale time-saver, they make more and
more sense the larger the app gets - and the purpose is to abstract the
specific of how something gets done.

Using your examples, if you write your application to use the IComparer
interface:

IComparer objMyComparer = new SomeClass();

Since SomeClass implements IComparer - the above is valid. Imagine that you
could have several different KINDS of comparers - and you would only need to
write your new classes to implement that same IComparer interface.

hope that helps..

" Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
news:uLBzK$kZDH A.2668@TK2MSFTN GP09.phx.gbl...[color=blue]
> Why does code derive from for example, IComparer
>
> ie,
>
> class SomeClass : IComparer
> {
> public SomeClass()
> {
> }
>
> public int Compare(object x, object y)
> {
> return someInt;
> }
> }
>
>
> When it just uses that and could have done without deriving ICompare[/color]
and[color=blue]
> got the same result.
>
> class SomeClass
> {
> public SomeClass()
> {
> }
>
> public int Compare(object x, object y)
> {
> return someInt;
> }
> }
>
> --
>
> Duncan McNutt
> Microsoft Product Deactivation Team
> --
>
>
>[/color]

[Duncan McNutt .[FTSE]]

Re: Interfaces

Yeah but why must that class implement ICompare when it can just as easily
make a public Compare (obj , obj) method and be the same.



--

Duncan McNutt
Microsoft Product Deactivation Team
--


"Ignacio Machin" <ignacio.mach in AT dot.state.fl.us > wrote in message
news:uL48cNlZDH A.3768@tk2msftn gp13.phx.gbl...[color=blue]
> Hi Duncan,
>
> You do not derive from an interface, you implement it, there is a[/color]
diference,[color=blue]
> an interface is like a template, it has no implementation it only assure
> that the classes that implement it have a predefined setof methods ( the
> interface ) , when you derive from a class you extend that class, add new
> functionality. you do not do that with an interface.
>
> Hope this help,
>
> --
> Ignacio Machin,
> ignacio.machin AT dot.state.fl.us
> Florida Department Of Transportation
>
>
> " Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
> news:uLBzK$kZDH A.2668@TK2MSFTN GP09.phx.gbl...[color=green]
> > Why does code derive from for example, IComparer
> >
> > ie,
> >
> > class SomeClass : IComparer
> > {
> > public SomeClass()
> > {
> > }
> >
> > public int Compare(object x, object y)
> > {
> > return someInt;
> > }
> > }
> >
> >
> > When it just uses that and could have done without deriving ICompare[/color]
> and[color=green]
> > got the same result.
> >
> > class SomeClass
> > {
> > public SomeClass()
> > {
> > }
> >
> > public int Compare(object x, object y)
> > {
> > return someInt;
> > }
> > }
> >
> > --
> >
> > Duncan McNutt
> > Microsoft Product Deactivation Team
> > --
> >
> >
> >[/color]
>
>[/color]

[Duncan McNutt .[FTSE]]

Re: Interfaces

yeah I know, i just wasnt thinking, caffine levels droped :D

But my question is, why implement ICompare when I can just as easily make
the method without reference to IComapre at all in the class.

What is the benifit.


--

Duncan McNutt
Microsoft Product Deactivation Team
--


"Ignacio Machin" <ignacio.mach in AT dot.state.fl.us > wrote in message
news:eAg#5QlZDH A.652@TK2MSFTNG P10.phx.gbl...[color=blue]
> Hi Duncan,
>
>
> I would suggest you something, if you have this kind of doubt, try it !![/color]
,[color=blue]
> do not missunderstand me, I believe that the best way to learn is
> experimenting, your code will not fail cause as I explained in the[/color]
previous[color=blue]
> post when you derive you are extending therefore the new class gets all[/color]
the[color=blue]
> parent's functionality.
>
> Hope this help,
>
> --
> Ignacio Machin,
> ignacio.machin AT dot.state.fl.us
> Florida Department Of Transportation
>
>
> " Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
> news:ekcmmBlZDH A.1940@TK2MSFTN GP10.phx.gbl...[color=green]
> > And another question...
> >
> > Because SomeClass derives from the IComparer interface
> >
> >
> > if i use SomeClass as a base of another like...
> >
> > class SomeNewClass : SomeClass
> > {
> > public SomeNewClass()
> > {
> > }
> > }
> >
> > Would that above fail due to no Compare method as SomeClass is derived[/color]
> from[color=green]
> > ICompare and it MUST implement Compare.. like..
> >
> > class SomeNewClass : SomeClass
> > {
> > public SomeNewClass()
> > {
> > }
> >
> > public int Compare(object x, object y)
> > {
> > return someInt;
> > }
> > }
> >
> > The above would work.
> >
> > Do i understand this correctly?
> >
> > --
> >
> > Duncan McNutt
> > Microsoft Product Deactivation Team
> > --
> >
> >
> > " Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
> > news:uLBzK$kZDH A.2668@TK2MSFTN GP09.phx.gbl...[color=darkred]
> > > Why does code derive from for example, IComparer
> > >
> > > ie,
> > >
> > > class SomeClass : IComparer
> > > {
> > > public SomeClass()
> > > {
> > > }
> > >
> > > public int Compare(object x, object y)
> > > {
> > > return someInt;
> > > }
> > > }
> > >
> > >
> > > When it just uses that and could have done without deriving[/color][/color][/color]
ICompare[color=blue][color=green]
> > and[color=darkred]
> > > got the same result.
> > >
> > > class SomeClass
> > > {
> > > public SomeClass()
> > > {
> > > }
> > >
> > > public int Compare(object x, object y)
> > > {
> > > return someInt;
> > > }
> > > }
> > >
> > > --
> > >
> > > Duncan McNutt
> > > Microsoft Product Deactivation Team
> > > --
> > >
> > >
> > >[/color]
> >
> >[/color]
>
>[/color]

[Duncan McNutt .[FTSE]]

Re: Interfaces

ahh ok, thanks that clears it up.

I just saw it in a small snipit of code on a little project and It just
didnt make sense why he used it for that example but yeah i can see the
benifit of that when scaling it up :D

So, would it be good practice to implement such interfaces where possible,
regardless of size, just for future or where basically I can see a specific
need for generic implementation?

--

Duncan McNutt
Microsoft Product Deactivation Team
--


"Frank Drebin" <noemail@imsick ofspam.com> wrote in message
news:Usp0b.2723 3$Vx2.12517799@ newssvr28.news. prodigy.com...[color=blue]
> The key element is that the purpose of an interface is that you can write
> your code to a generic "interface" ..
>
> For example, say you have a Windows app that needs to connect to a
> datasource. That datasource could be a real database, a remote web service
> and also an offline file. But you want to abstract HOW the datasource gets
> it's data. If you couldn't abstract it, you'd have to write 3 versions of
> code mixed in with your main application - to do this.
>
> but instead, you could write your application to use the IDataAccess
> interface (this is an interface you write, it has Connect()[/color]
Authenticate(),[color=blue]
> etc)..
>
> Then you have classes such as Database, WebService and OfflineAccess that
> implement that interface.
>
> So Interfaces aren't so much a small-scale time-saver, they make more and
> more sense the larger the app gets - and the purpose is to abstract the
> specific of how something gets done.
>
> Using your examples, if you write your application to use the IComparer
> interface:
>
> IComparer objMyComparer = new SomeClass();
>
> Since SomeClass implements IComparer - the above is valid. Imagine that[/color]
you[color=blue]
> could have several different KINDS of comparers - and you would only need[/color]
to[color=blue]
> write your new classes to implement that same IComparer interface.
>
> hope that helps..
>
> " Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
> news:uLBzK$kZDH A.2668@TK2MSFTN GP09.phx.gbl...[color=green]
> > Why does code derive from for example, IComparer
> >
> > ie,
> >
> > class SomeClass : IComparer
> > {
> > public SomeClass()
> > {
> > }
> >
> > public int Compare(object x, object y)
> > {
> > return someInt;
> > }
> > }
> >
> >
> > When it just uses that and could have done without deriving ICompare[/color]
> and[color=green]
> > got the same result.
> >
> > class SomeClass
> > {
> > public SomeClass()
> > {
> > }
> >
> > public int Compare(object x, object y)
> > {
> > return someInt;
> > }
> > }
> >
> > --
> >
> > Duncan McNutt
> > Microsoft Product Deactivation Team
> > --
> >
> >
> >[/color]
>
>[/color]

[Peter Vidler]

Re: Interfaces

Hi,
[color=blue]
> Whats to stop me just coding a public int Compare(object x, object y)[/color]

Because my CompareStuff method ("public int CompareStuff(IC omparer[]
stuff)") couldn't use your class unless you implement IComparer.

Hope that syntax was correct :)

Pete

[Ashish]

Re: Interfaces

Read some OOP book before starting on C#. Advise of a wellwisher...
Ashish

" Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
news:uLBzK$kZDH A.2668@TK2MSFTN GP09.phx.gbl...[color=blue]
> Why does code derive from for example, IComparer
>
> ie,
>
> class SomeClass : IComparer
> {
> public SomeClass()
> {
> }
>
> public int Compare(object x, object y)
> {
> return someInt;
> }
> }
>
>
> When it just uses that and could have done without deriving ICompare[/color]
and[color=blue]
> got the same result.
>
> class SomeClass
> {
> public SomeClass()
> {
> }
>
> public int Compare(object x, object y)
> {
> return someInt;
> }
> }
>
> --
>
> Duncan McNutt
> Microsoft Product Deactivation Team
> --
>
>
>[/color]

[Frank Drebin]

Re: Interfaces

Since I've started developing in OO - I've been learning that the more you
can abstract, the better...

So it really is just a trade-off of - how much time (now, and in the future)
will writing an interface save me.. versus how long will it take me to
write.

But as a general rule, I'm a big fan abstracting as much as possible,
whenever possible...

" Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
news:%23xyXjTlZ DHA.1680@tk2msf tngp13.phx.gbl. ..[color=blue]
> ahh ok, thanks that clears it up.
>
> I just saw it in a small snipit of code on a little project and It just
> didnt make sense why he used it for that example but yeah i can see the
> benifit of that when scaling it up :D
>
> So, would it be good practice to implement such interfaces where possible,
> regardless of size, just for future or where basically I can see a[/color]
specific[color=blue]
> need for generic implementation?
>
> --
>
> Duncan McNutt
> Microsoft Product Deactivation Team
> --
>
>
> "Frank Drebin" <noemail@imsick ofspam.com> wrote in message
> news:Usp0b.2723 3$Vx2.12517799@ newssvr28.news. prodigy.com...[color=green]
> > The key element is that the purpose of an interface is that you can[/color][/color]
write[color=blue][color=green]
> > your code to a generic "interface" ..
> >
> > For example, say you have a Windows app that needs to connect to a
> > datasource. That datasource could be a real database, a remote web[/color][/color]
service[color=blue][color=green]
> > and also an offline file. But you want to abstract HOW the datasource[/color][/color]
gets[color=blue][color=green]
> > it's data. If you couldn't abstract it, you'd have to write 3 versions[/color][/color]
of[color=blue][color=green]
> > code mixed in with your main application - to do this.
> >
> > but instead, you could write your application to use the IDataAccess
> > interface (this is an interface you write, it has Connect()[/color]
> Authenticate(),[color=green]
> > etc)..
> >
> > Then you have classes such as Database, WebService and OfflineAccess[/color][/color]
that[color=blue][color=green]
> > implement that interface.
> >
> > So Interfaces aren't so much a small-scale time-saver, they make more[/color][/color]
and[color=blue][color=green]
> > more sense the larger the app gets - and the purpose is to abstract the
> > specific of how something gets done.
> >
> > Using your examples, if you write your application to use the IComparer
> > interface:
> >
> > IComparer objMyComparer = new SomeClass();
> >
> > Since SomeClass implements IComparer - the above is valid. Imagine that[/color]
> you[color=green]
> > could have several different KINDS of comparers - and you would only[/color][/color]
need[color=blue]
> to[color=green]
> > write your new classes to implement that same IComparer interface.
> >
> > hope that helps..
> >
> > " Duncan McNutt .[FTSE]" <pitmaster@127. 0.0.701> wrote in message
> > news:uLBzK$kZDH A.2668@TK2MSFTN GP09.phx.gbl...[color=darkred]
> > > Why does code derive from for example, IComparer
> > >
> > > ie,
> > >
> > > class SomeClass : IComparer
> > > {
> > > public SomeClass()
> > > {
> > > }
> > >
> > > public int Compare(object x, object y)
> > > {
> > > return someInt;
> > > }
> > > }
> > >
> > >
> > > When it just uses that and could have done without deriving[/color][/color][/color]
ICompare[color=blue][color=green]
> > and[color=darkred]
> > > got the same result.
> > >
> > > class SomeClass
> > > {
> > > public SomeClass()
> > > {
> > > }
> > >
> > > public int Compare(object x, object y)
> > > {
> > > return someInt;
> > > }
> > > }
> > >
> > > --
> > >
> > > Duncan McNutt
> > > Microsoft Product Deactivation Team
> > > --
> > >
> > >
> > >[/color]
> >
> >[/color]
>
>[/color]

[Jon Skeet]

Re: Interfaces

Duncan McNutt .[FTSE] <pitmaster@127. 0.0.701> wrote:[color=blue]
> Why does code derive from for example, IComparer
>
> ie,
>
> class SomeClass : IComparer
> {
> public SomeClass()
> {
> }
>
> public int Compare(object x, object y)
> {
> return someInt;
> }
> }
>
>
> When it just uses that and could have done without deriving ICompare and
> got the same result.[/color]

No you didn't. You can't use an instance of SomeClass to provide the
comparisons for Array.Sort, for instance, unless is implements
IComparer.

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet/

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