RE: [flexcoders] Returning 'this' from an overridden method?
Well, it really depends on the ECMA working group. I would like to get
it in, and I will push for it, and I imagine that others will as well.
-Sho
From: flexcoders@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Ralf Bokelberg
Sent: Wednesday, February 07, 2007 11:10 AM
To: flexcoders@yahoogroups.com
Subject: Re: [flexcoders] Returning 'this' from an overridden
method?
Nice to know the name of this feature.
Just lately somebody asked me the same question.
He also came from a Java background.
Any chance we will see it in the future?
Cheers,
Ralf.
On 2/7/07, Sho Kuwamoto <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> > wrote:
The short answer is that there is no way to do what you
want for the time being.
What you are looking for is a language feature called
"covariant return types". In certain languages (C++, Java) you can have
your subclass redefine the type that is returned by a method.
This would be a great thing to get into the AS language,
but it is not there now. There are further wrinkles when you consider
how you would extend properties in a similar way (I wrote about the
issues at http://kuwamoto.org/2007/01/22/covariant-property-types/
<http://kuwamoto.org/2007/01/22/covariant-property-types/> ).
Cheers,
-Sho
From: flexcoders@yahoogroups.com
[mailto:flexcoders@yahoogroups.com <http://yahoogroups.com> ] On Behalf
Of David_Stafford
Sent: Tuesday, February 06, 2007 6:13 PM
To: flexcoders@yahoogroups.com
Subject: [flexcoders] Returning 'this' from an
overridden method?
Please pardon this simple-minded question from
an AS3 novice.
My base class often returns 'this' from methods
which makes it
convenient to write code like:
camera.move( 10, 12 ).rotateX( 45 ).rotateY( 90
);
The problem comes when code extends the base
class and overrides one
of these functions. The compiler insists,
correctly, that the return
type of an overriding function must match the
one in the base class.
What I want to do is return the 'this' object
that is of the type of
the derived class. Is this possible?
The following is a contrived example to
demonstrate. It won't
compile because the overridden function in the
derived class wants to
return a type of MyCamera rather than Camera:
public class Camera
{
var x:int = 0;
var y:int = 0;
public function move( x:int, y:int ) :Camera
{
this.x += x;
this.y += y;
return( this );
}
}
public class MyCamera extends Camera
{
override public function move( x:int, y:int )
:MyCamera
{
super.move( x, y );
if( x < 0 ) x = 0;
if( y < 0 ) y = 0;
return( this );
}
}
--
Ralf Bokelberg <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> >
Flex & Flash Consultant based in Cologne/Germany
Phone +49 (0) 221 530 15 35
RE: [flexcoders] Returning 'this' from an overridden method?
That's up to the ECMAScxript committee. But since I think an Adobe
engineer chairs or co-chairs it, we have some influence.
- Gordon
From: flexcoders@yahoogroups.com [mailto:[EMAIL PROTECTED] On
Behalf Of Ralf Bokelberg
Sent: Wednesday, February 07, 2007 11:10 AM
To: flexcoders@yahoogroups.com
Subject: Re: [flexcoders] Returning 'this' from an overridden method?
Nice to know the name of this feature.
Just lately somebody asked me the same question.
He also came from a Java background.
Any chance we will see it in the future?
Cheers,
Ralf.
On 2/7/07, Sho Kuwamoto <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
> wrote:
The short answer is that there is no way to do what you want for the
time being.
What you are looking for is a language feature called "covariant return
types". In certain languages (C++, Java) you can have your subclass
redefine the type that is returned by a method.
This would be a great thing to get into the AS language, but it is not
there now. There are further wrinkles when you consider how you would
extend properties in a similar way (I wrote about the issues at
http://kuwamoto.org/2007/01/22/covariant-property-types/
<http://kuwamoto.org/2007/01/22/covariant-property-types/> ).
Cheers,
-Sho
From: flexcoders@yahoogroups.com
[mailto:flexcoders@yahoogroups.com <http://yahoogroups.com> ] On Behalf
Of David_Stafford
Sent: Tuesday, February 06, 2007 6:13 PM
To: flexcoders@yahoogroups.com
Subject: [flexcoders] Returning 'this' from an overridden
method?
Please pardon this simple-minded question from an AS3 novice.
My base class often returns 'this' from methods which makes it
convenient to write code like:
camera.move( 10, 12 ).rotateX( 45 ).rotateY( 90 );
The problem comes when code extends the base class and overrides
one
of these functions. The compiler insists, correctly, that the
return
type of an overriding function must match the one in the base
class.
What I want to do is return the 'this' object that is of the
type of
the derived class. Is this possible?
The following is a contrived example to demonstrate. It won't
compile because the overridden function in the derived class
wants to
return a type of MyCamera rather than Camera:
public class Camera
{
var x:int = 0;
var y:int = 0;
public function move( x:int, y:int ) :Camera
{
this.x += x;
this.y += y;
return( this );
}
}
public class MyCamera extends Camera
{
override public function move( x:int, y:int ) :MyCamera
{
super.move( x, y );
if( x < 0 ) x = 0;
if( y < 0 ) y = 0;
return( this );
}
}
--
Ralf Bokelberg <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> >
Flex & Flash Consultant based in Cologne/Germany
Phone +49 (0) 221 530 15 35
Re: [flexcoders] Returning 'this' from an overridden method?
Nice to know the name of this feature.
Just lately somebody asked me the same question.
He also came from a Java background.
Any chance we will see it in the future?
Cheers,
Ralf.
On 2/7/07, Sho Kuwamoto <[EMAIL PROTECTED]> wrote:
The short answer is that there is no way to do what you want for the
time being.
What you are looking for is a language feature called "covariant return
types". In certain languages (C++, Java) you can have your subclass redefine
the type that is returned by a method.
This would be a great thing to get into the AS language, but it is not
there now. There are further wrinkles when you consider how you would extend
properties in a similar way (I wrote about the issues at
http://kuwamoto.org/2007/01/22/covariant-property-types/).
Cheers,
-Sho
--
*From:* flexcoders@yahoogroups.com [mailto:[EMAIL PROTECTED] *On
Behalf Of *David_Stafford
*Sent:* Tuesday, February 06, 2007 6:13 PM
*To:* flexcoders@yahoogroups.com
*Subject:* [flexcoders] Returning 'this' from an overridden method?
Please pardon this simple-minded question from an AS3 novice.
My base class often returns 'this' from methods which makes it
convenient to write code like:
camera.move( 10, 12 ).rotateX( 45 ).rotateY( 90 );
The problem comes when code extends the base class and overrides one
of these functions. The compiler insists, correctly, that the return
type of an overriding function must match the one in the base class.
What I want to do is return the 'this' object that is of the type of
the derived class. Is this possible?
The following is a contrived example to demonstrate. It won't
compile because the overridden function in the derived class wants to
return a type of MyCamera rather than Camera:
public class Camera
{
var x:int = 0;
var y:int = 0;
public function move( x:int, y:int ) :Camera
{
this.x += x;
this.y += y;
return( this );
}
}
public class MyCamera extends Camera
{
override public function move( x:int, y:int ) :MyCamera
{
super.move( x, y );
if( x < 0 ) x = 0;
if( y < 0 ) y = 0;
return( this );
}
}
--
Ralf Bokelberg <[EMAIL PROTECTED]>
Flex & Flash Consultant based in Cologne/Germany
Phone +49 (0) 221 530 15 35
RE: [flexcoders] Returning 'this' from an overridden method?
The short answer is that there is no way to do what you want for the
time being.
What you are looking for is a language feature called "covariant return
types". In certain languages (C++, Java) you can have your subclass
redefine the type that is returned by a method.
This would be a great thing to get into the AS language, but it is not
there now. There are further wrinkles when you consider how you would
extend properties in a similar way (I wrote about the issues at
http://kuwamoto.org/2007/01/22/covariant-property-types/).
Cheers,
-Sho
From: flexcoders@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of David_Stafford
Sent: Tuesday, February 06, 2007 6:13 PM
To: flexcoders@yahoogroups.com
Subject: [flexcoders] Returning 'this' from an overridden
method?
Please pardon this simple-minded question from an AS3 novice.
My base class often returns 'this' from methods which makes it
convenient to write code like:
camera.move( 10, 12 ).rotateX( 45 ).rotateY( 90 );
The problem comes when code extends the base class and overrides
one
of these functions. The compiler insists, correctly, that the
return
type of an overriding function must match the one in the base
class.
What I want to do is return the 'this' object that is of the
type of
the derived class. Is this possible?
The following is a contrived example to demonstrate. It won't
compile because the overridden function in the derived class
wants to
return a type of MyCamera rather than Camera:
public class Camera
{
var x:int = 0;
var y:int = 0;
public function move( x:int, y:int ) :Camera
{
this.x += x;
this.y += y;
return( this );
}
}
public class MyCamera extends Camera
{
override public function move( x:int, y:int ) :MyCamera
{
super.move( x, y );
if( x < 0 ) x = 0;
if( y < 0 ) y = 0;
return( this );
}
}
Re: [flexcoders] Returning 'this' from an overridden method?
Hi David,
I to am an AS3 novice. Wrote my first(trivial) action script file about
an hour ago. :)
A couple of ideas. Not sure if they will be of much help to you, but
incase you hadnt considered them already..
. you could return the value returned by the call to super.
ie)
Camera c = super.move;
//// some local x,y stuff
return c;
. you could use an interface as the return value. eg) interface ICamera
would define the move and rotate methods and return an ICamera and your
Camera classes would implement ICamera.
I realise that these options do not do what you asked for, but you might
find one of these is an acceptable alternative.
HTH.
cheers,
- shaun
David_Stafford wrote:
> Please pardon this simple-minded question from an AS3 novice.
>
> My base class often returns 'this' from methods which makes it
> convenient to write code like:
>
> camera.move( 10, 12 ).rotateX( 45 ).rotateY( 90 );
>
> The problem comes when code extends the base class and overrides one
> of these functions. The compiler insists, correctly, that the return
> type of an overriding function must match the one in the base class.
> What I want to do is return the 'this' object that is of the type of
> the derived class. Is this possible?
>
> The following is a contrived example to demonstrate. It won't
> compile because the overridden function in the derived class wants to
> return a type of MyCamera rather than Camera:
>
>
> public class Camera
> {
> var x:int = 0;
> var y:int = 0;
>
> public function move( x:int, y:int ) :Camera
> {
> this.x += x;
> this.y += y;
>
> return( this );
> }
> }
>
> public class MyCamera extends Camera
> {
> override public function move( x:int, y:int ) :MyCamera
> {
> super.move( x, y );
>
> if( x < 0 ) x = 0;
> if( y < 0 ) y = 0;
>
> return( this );
> }
> }
Re: [flexcoders] Returning 'this' from an overridden method?
- Original Message -
From: "David_Stafford" <[EMAIL PROTECTED]>
To:
Sent: Wednesday, February 07, 2007 2:12 AM
Subject: [flexcoders] Returning 'this' from an overridden method?
> Please pardon this simple-minded question from an AS3 novice.
>
> My base class often returns 'this' from methods which makes it
> convenient to write code like:
>
> camera.move( 10, 12 ).rotateX( 45 ).rotateY( 90 );
>
> The problem comes when code extends the base class and overrides one
> of these functions. The compiler insists, correctly, that the return
> type of an overriding function must match the one in the base class.
> What I want to do is return the 'this' object that is of the type of
> the derived class. Is this possible?
>
> The following is a contrived example to demonstrate. It won't
> compile because the overridden function in the derived class wants to
> return a type of MyCamera rather than Camera:
This is the correct behaviour. The derived class is MyCamera and any
reference to this, either in the derived class or it's parent will be
working with an object of class MyCamera not Camera.
Make the return type Camera, then it will work. You will be returning an
object reference of class Camera, but in fact it is an object reference to
an object of class MyCamera. You can then cast it elsewhere as a 'MyCamera'
in the application.
The problem is that you are trying to change the signature of the method
that you are overriding.
Paul
> public class Camera
> {
> var x:int = 0;
> var y:int = 0;
>
> public function move( x:int, y:int ) :Camera
> {
> this.x += x;
> this.y += y;
>
> return( this );
> }
> }
>
> public class MyCamera extends Camera
> {
> override public function move( x:int, y:int ) :MyCamera
> {
> super.move( x, y );
>
> if( x < 0 ) x = 0;
> if( y < 0 ) y = 0;
>
> return( this );
> }
> }
>
>
>
>
>
> --
> Flexcoders Mailing List
> FAQ: http://groups.yahoo.com/group/flexcoders/files/flexcodersFAQ.txt
> Search Archives: http://www.mail-archive.com/flexcoders%40yahoogroups.com
> Yahoo! Groups Links
>
>
>
>
[flexcoders] Returning 'this' from an overridden method?
Please pardon this simple-minded question from an AS3 novice.
My base class often returns 'this' from methods which makes it
convenient to write code like:
camera.move( 10, 12 ).rotateX( 45 ).rotateY( 90 );
The problem comes when code extends the base class and overrides one
of these functions. The compiler insists, correctly, that the return
type of an overriding function must match the one in the base class.
What I want to do is return the 'this' object that is of the type of
the derived class. Is this possible?
The following is a contrived example to demonstrate. It won't
compile because the overridden function in the derived class wants to
return a type of MyCamera rather than Camera:
public class Camera
{
var x:int = 0;
var y:int = 0;
public function move( x:int, y:int ) :Camera
{
this.x += x;
this.y += y;
return( this );
}
}
public class MyCamera extends Camera
{
override public function move( x:int, y:int ) :MyCamera
{
super.move( x, y );
if( x < 0 ) x = 0;
if( y < 0 ) y = 0;
return( this );
}
}
