digitalmars.D - Make 'abstract' mandatory if the class is intended to be abstract,
- Ary Borenszweig (40/40) Apr 28 2008 A class can either be abstract or not abstract. Currently in D, if you
- Christopher Wright (4/30) Apr 28 2008 You have my support. With the new hiding as an error thing, my faith in
- Graham St Jack (2/54) Apr 28 2008
- Gide Nwawudu (3/43) Apr 29 2008 vote++
- Bruno Medeiros (4/4) Apr 29 2008 vote +1
A class can either be abstract or not abstract. Currently in D, if you
don't mark a class as abstract, it can still be it if it contains an
abstract method:
class Foo {
abstract void someAbstract();
void nonAbstract() {
}
}
When designing a class, you have in mind whether the class is going to
be abstract or not. If it's not going to be abstract, you want the
compiler to help you by telling you "You made a mistake. This class is
still abstract because you didn't implement method foo".
So I want to extend Foo with a class Bar, but I want Bar to be not abstract.
class Bar : Foo {
}
I compile, and it gives no error, of course. But I want there to be an
error there. The only way I can get an error is by making a dummy
function that instantiates Bar:
void blah() {
Bar bar = new Bar();
}
main.d(14): Error: cannot create instance of abstract class Bar
main.d(14): Error: function someAbstract is abstract
The problems with this appraoch are two:
- You have to make a dummy function to check whether you implemented
Bar correctly.
- You get two errors for each instantiation of Bar, if it's abstract
(ugly).
Why not make "abstract" mandatory for a class if it's intended to be
abstract, and the absence of "abstract" to mean "not abstract"? Java
works this way, and I think it is for the reasons I mentioned.
Another advantage is that just by seeing the start of class definition
you can tell whether a class is abstract or not. You don't have to see
if any method is marked as abstract, or go to the superclasses to see if
there is a method that is still not implemented.
(also, it would be nice if the compiler could tell you all the methods
that still need an implementation, rather than just one)
Apr 28 2008
Christopher Wright <dhasenan gmail.com>
Ary Borenszweig wrote:
A class can either be abstract or not abstract. Currently in D, if you
don't mark a class as abstract, it can still be it if it contains an
abstract method:
class Foo {
abstract void someAbstract();
void nonAbstract() {
}
}
When designing a class, you have in mind whether the class is going to
be abstract or not. If it's not going to be abstract, you want the
compiler to help you by telling you "You made a mistake. This class is
still abstract because you didn't implement method foo".
So I want to extend Foo with a class Bar, but I want Bar to be not
abstract.
class Bar : Foo {
}
I compile, and it gives no error, of course. But I want there to be an
error there.
You have my support. With the new hiding as an error thing, my faith in
Walter thinking of catching stupid errors is shored up, and I have a
reasonable hope that this suggestion will succeed.
Apr 28 2008
I agree
On Mon, 28 Apr 2008 10:11:23 -0300, Ary Borenszweig wrote:
A class can either be abstract or not abstract. Currently in D, if you
don't mark a class as abstract, it can still be it if it contains an
abstract method:
class Foo {
abstract void someAbstract();
void nonAbstract() {
}
}
When designing a class, you have in mind whether the class is going to
be abstract or not. If it's not going to be abstract, you want the
compiler to help you by telling you "You made a mistake. This class is
still abstract because you didn't implement method foo".
So I want to extend Foo with a class Bar, but I want Bar to be not
abstract.
class Bar : Foo {
}
I compile, and it gives no error, of course. But I want there to be an
error there. The only way I can get an error is by making a dummy
function that instantiates Bar:
void blah() {
Bar bar = new Bar();
}
main.d(14): Error: cannot create instance of abstract class Bar
main.d(14): Error: function someAbstract is abstract
The problems with this appraoch are two:
- You have to make a dummy function to check whether you implemented
Bar correctly.
- You get two errors for each instantiation of Bar, if it's abstract
(ugly).
Why not make "abstract" mandatory for a class if it's intended to be
abstract, and the absence of "abstract" to mean "not abstract"? Java
works this way, and I think it is for the reasons I mentioned.
Another advantage is that just by seeing the start of class definition
you can tell whether a class is abstract or not. You don't have to see
if any method is marked as abstract, or go to the superclasses to see if
there is a method that is still not implemented.
(also, it would be nice if the compiler could tell you all the methods
that still need an implementation, rather than just one)
Apr 28 2008
vote++
On Mon, 28 Apr 2008 10:11:23 -0300, Ary Borenszweig
<ary esperanto.org.ar> wrote:
A class can either be abstract or not abstract. Currently in D, if you
don't mark a class as abstract, it can still be it if it contains an
abstract method:
class Foo {
abstract void someAbstract();
void nonAbstract() {
}
}
When designing a class, you have in mind whether the class is going to
be abstract or not. If it's not going to be abstract, you want the
compiler to help you by telling you "You made a mistake. This class is
still abstract because you didn't implement method foo".
So I want to extend Foo with a class Bar, but I want Bar to be not abstract.
class Bar : Foo {
}
I compile, and it gives no error, of course. But I want there to be an
error there. The only way I can get an error is by making a dummy
function that instantiates Bar:
void blah() {
Bar bar = new Bar();
}
main.d(14): Error: cannot create instance of abstract class Bar
main.d(14): Error: function someAbstract is abstract
The problems with this appraoch are two:
- You have to make a dummy function to check whether you implemented
Bar correctly.
- You get two errors for each instantiation of Bar, if it's abstract
(ugly).
Why not make "abstract" mandatory for a class if it's intended to be
abstract, and the absence of "abstract" to mean "not abstract"? Java
works this way, and I think it is for the reasons I mentioned.
Another advantage is that just by seeing the start of class definition
you can tell whether a class is abstract or not. You don't have to see
if any method is marked as abstract, or go to the superclasses to see if
there is a method that is still not implemented.
(also, it would be nice if the compiler could tell you all the methods
that still need an implementation, rather than just one)
Apr 29 2008