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Partially instantiated classes ?!
Wed, 2009-01-14, 11:29
Hello, I am trying to do something that "could" be named partially
instantiation ...
This is the kind of thing I want to do, but some pieces of code
are missing :
// Written by me
abstract class Foo {
val needed: String
def doSomething: String
}
object Constructor {
val theNeeded = "needed"
def apply(aPartiallyInstantiatedFoo :...) : Foo = {
... aPartiallyInstantiatedFoo ... { val needed = theNeeded }
}
}
// Written by other people :
abstract class Bar extends Foo {
def doSomething = needed
}
object Example extends Application {
Constructor(... Bar ...).doSomething
}
The idea is that I want the people extending Foo to be able to
use the needed field of it, without adding extra parameters to the
extending class or its functions.
And I want people to be able to construct a Foo with their
implementation without bothering with the needed field.
Using a Constructor object is my idea, maybe it is not a good one
...
I know I can do something like that with partial function, but what about
object ? I was hoping someone had an idea :)
Thanks you for any help,
Victor
Wed, 2009-01-14, 16:47
#2
Re: Partially instantiated classes ?!
On Wed, Jan 14, 2009 at 04:28:36PM +0100, Florian Hars wrote:
> Victor NOEL schrieb:
> > Hello, I am trying to do something that "could" be named partially
> > instantiation ...
>
> But it *is* called mixin composition, if I understand your problem
> correctly:
Yes, with the specification of the problem I gave, but it looks
like I forgot to say something important :
I don't know what will be the value of needed when Bar will be
written.
I will *only* know that just needed will not be specified (or I
want my code to force things to be like that :)
For now, the only thing I can do is :
abstract class Foo(needed: String) {
def doSomething: String
}
class Bar(needed: String) extends Foo(needed) {
def doSomething = needed
}
object Constructor {
val needed = "needed"
def apply(f: String => Foo) : Foo = {
f(needed)
}
}
and then :
> Constructor(Bar(_))
But I don't like the idea of having this needed travelling in the
constructors, so I thought of a solution with abstract members
(which doesn't work :)
Thanks for your help anyway, it makes me think and maybe it will
permit me to find a solution ...
Victor
Victor NOEL schrieb:
> Hello, I am trying to do something that "could" be named partially
> instantiation ...
But it *is* called mixin composition, if I understand your problem
correctly:
// Your Code:
trait Foo {
val needed: String
def doSomething: String
}
trait NoNeed {
val needed = "needed"
}
// Somebody else's code
class Bar extends Foo with NoNeed {
def doSomething = needed
}
And then :
scala> new Bar doSomething
res1: java.lang.String = needed
- Florian