Indexed properties

[Konstantin Kipa]

Hi

Does anyone know how to create an indexed property?

For example, I want to have a class MyClass and be able to access one of the
properties as

MyClass b = new MyClass();
MyClass.myarray[1] = 345;

is is possible. I read through documentation about Indexers but this is not
what I want.

Konstantin

[Roberto Martinez-Brunet]

Just expose a public array. Or an array property.

Roberto

"Konstantin Kipa" <konstantin@metaobjects.net> wrote in message
news:3a38dd52@news.devx.com...
> Hi
>
> Does anyone know how to create an indexed property?
>
> For example, I want to have a class MyClass and be able to access one of
the
> properties as
>
> MyClass b = new MyClass();
> MyClass.myarray[1] = 345;
>
> is is possible. I read through documentation about Indexers but this is
not
> what I want.
>
> Konstantin
>
>
>
>
>

[David Bayley]

Konstantin,

You can declare the property as an array, System.Collections.ArrayList, or a
custom collection derived from ArrayList, as in...

using System.Collections;

public class MyClass {

private int[] myArray = new int[100];
private ArrayList myArrayList = new ArrayList();
private Collection myCollection = new Collection;

public int[] MyArray {
get { return myArray; }
}

public ArrayList MyArrayList {
get { return myArrayList; }
}

public Collection MyCollection{
get { return myCollection; }
}

public class Collection : ArrayList {
public override object this[int index] {
get { return base.Item[index]; }
set { base.Item[index] = value; }
}
}

}

// usage...
MyClass b = new MyClass();
int n;

b.MyArray[50] = 345;
n = b.MyArray[50];

b.MyArrayList.Add(10);
b.MyArrayList.Add(20);
b.MyArrayList[1] = 30;
n = (int)b.MyArrayList[1];

b.MyCollection.Add(10);
b.MyCollection.Add(20);
b.MyCollection[1] = 30;
n = (int)b.MyCollection[1];


--
David.

Konstantin Kipa <konstantin@metaobjects.net> wrote in message
news:3a38dd52@news.devx.com...
> Hi
>
> Does anyone know how to create an indexed property?
>
> For example, I want to have a class MyClass and be able to access one of
the
> properties as
>
> MyClass b = new MyClass();
> MyClass.myarray[1] = 345;
>
> is is possible. I read through documentation about Indexers but this is
not
> what I want.
>
> Konstantin
>
>
>
>
>

[Jeff Peil]

Konstantin,

C# does not support indexed properties.

It does support an indexer for a class, but it sounds like you are already
familiar with the subtle difference.

If the type of the property named "myarray" supported an indexer, for
example if it were an ArrayList, then you would be able to index on it.

"Konstantin Kipa" <konstantin@metaobjects.net> wrote in message
news:3a38dd52@news.devx.com...
> Hi
>
> Does anyone know how to create an indexed property?
>
> For example, I want to have a class MyClass and be able to access one of
the
> properties as
>
> MyClass b = new MyClass();
> MyClass.myarray[1] = 345;
>
> is is possible. I read through documentation about Indexers but this is
not
> what I want.

[Jonathan Allen]

> C# does not support indexed properties.

Well that sucks. I am (almost) surprised that something so simple to do in
VB.Net is impossible in C#.

--
Jonathan Allen


"Jeff Peil" <jpeil@bigfoot.com> wrote in message
news:3a390a84@news.devx.com...
> Konstantin,
>
> C# does not support indexed properties.
>
> It does support an indexer for a class, but it sounds like you are already
> familiar with the subtle difference.
>
> If the type of the property named "myarray" supported an indexer, for
> example if it were an ArrayList, then you would be able to index on it.
>
> "Konstantin Kipa" <konstantin@metaobjects.net> wrote in message
> news:3a38dd52@news.devx.com...
> > Hi
> >
> > Does anyone know how to create an indexed property?
> >
> > For example, I want to have a class MyClass and be able to access one of
> the
> > properties as
> >
> > MyClass b = new MyClass();
> > MyClass.myarray[1] = 345;
> >
> > is is possible. I read through documentation about Indexers but this is
> not
> > what I want.
>
>
>

[Jeff Peil]

"Jonathan Allen" <greywolfcs@bigfoot.com> wrote in message
news:3a393d81@news.devx.com...
> > C# does not support indexed properties.
>
> Well that sucks. I am (almost) surprised that something so simple to do in
> VB.Net is impossible in C#.

Not like it isn't possible to create a synthetic equivalent as follows
(though I wouldn't suggest doing so, imo it's far better to stick with a
language's common conventions.)

public class Foo
{
public class <PropName>IndexImpl
{
Foo outer;
internal IndexedProp(Foo container) { outer = container; }
public <Type> this[<indexing params>] {
get { return outer.Get<PropName>(<indexing params>);}
set { outer.Set<PropName>(<indexing params>, value);}
}
public <PropName>IndexImpl <PropName> { get { return new
<PropName>IndexImpl(this); } }
private <Type> Get<PropName>(<indexing params>) {/*...*/}
private void Set<PropName>(<indexing params>, <Type> value) {/*...*/}
}

[Jonathan Allen]

>imo it's far better to stick with a language's common conventions

I agree.

When it comes down to messy work arounds or complaining until the language
supports it, I prefer the later.

--
Jonathan Allen


"Jeff Peil" <jpeil@bigfoot.com> wrote in message
news:3a394619$1@news.devx.com...
>
> "Jonathan Allen" <greywolfcs@bigfoot.com> wrote in message
> news:3a393d81@news.devx.com...
> > > C# does not support indexed properties.
> >
> > Well that sucks. I am (almost) surprised that something so simple to do
in
> > VB.Net is impossible in C#.
>
> Not like it isn't possible to create a synthetic equivalent as follows
> (though I wouldn't suggest doing so, imo it's far better to stick with a
> language's common conventions.)
>
> public class Foo
> {
> public class <PropName>IndexImpl
> {
> Foo outer;
> internal IndexedProp(Foo container) { outer = container; }
> public <Type> this[<indexing params>] {
> get { return outer.Get<PropName>(<indexing params>);}
> set { outer.Set<PropName>(<indexing params>, value);}
> }
> public <PropName>IndexImpl <PropName> { get { return new
> <PropName>IndexImpl(this); } }
> private <Type> Get<PropName>(<indexing params>) {/*...*/}
> private void Set<PropName>(<indexing params>, <Type> value) {/*...*/}
> }
>
>

[Konstantin Kipa]

Hi

The interesting thing is, what is the standard pattern to do this? For
example, I want to create read-only indexed property and do some
calculations on get {} method. How can I do this?

The pattern was - I had a private variable (array or collection) and access
this variable from my read-only indexed property.

Any ideas?

Thanks in advance

Konstantin Kipa

[Jeff Peil]

The standard pattern in C# is to use a readonly indexer.

"Konstantin Kipa" <konstantin@metaobjects.net> wrote in message
news:3a39e24e@news.devx.com...
> Hi
>
> The interesting thing is, what is the standard pattern to do this? For
> example, I want to create read-only indexed property and do some
> calculations on get {} method. How can I do this?
>
> The pattern was - I had a private variable (array or collection) and
access
> this variable from my read-only indexed property.
>
> Any ideas?
>
> Thanks in advance
>
> Konstantin Kipa
>
>

[Konstantin Kipa]

> The standard pattern in C# is to use a readonly indexer.

Right. How can I acces from indexer to a private variable in a class

Say, we have a class

public class Foo
{
private ArrayList arrayList;

// this property has to be an indexer as you said
public MyIndexer readonlyproperty
{
get;
}
}

Ok. Indexer would be a different class and should have an acces to arrayList
private variable in the class Foo. How is it possible? If we talking about
some variable inside Indexer class itself, class Foo has to have access to
this variable. BUT that means, I shoud give this variable higher level of
visibility rather than private. Which VERY bad for safety.

?!?

>
> "Konstantin Kipa" <konstantin@metaobjects.net> wrote in message
> news:3a39e24e@news.devx.com...
> > Hi
> >
> > The interesting thing is, what is the standard pattern to do this? For
> > example, I want to create read-only indexed property and do some
> > calculations on get {} method. How can I do this?
> >
> > The pattern was - I had a private variable (array or collection) and
> access
> > this variable from my read-only indexed property.
> >
> > Any ideas?
> >
> > Thanks in advance
> >
> > Konstantin Kipa
> >
> >
>
>

[David Bayley]

Konstantin,

Either, use up the one and only "indexer" available on Foo...

public class Foo {
private ArrayList arrayList;
public int this[int index] {
get { return (int)arrayList[index]; }
}
}
// use with "i = foo[5];"

Or write you're own nested class, and pass the arrayList to the
constructor...

public class Foo {
private ArrayList arrayList = new ArrayList();
private Indexer myIndexer = new Indexer(arrayList);

public Indexer MyIndexer {
get { return myIndexer; }
}

public class Indexer {
private ArrayList arrayList;
internal Indexer(ArrayList arrayList) {
this.arrayList = arrayList;
}
public int this[int index] {
get { return (int)arrayList[index]; }
}
}

}
// use with "i = foo.MyIndexer[5];"


Konstantin Kipa <konstantin@metaobjects.net> wrote in message
news:3a3a005e$1@news.devx.com...
> > The standard pattern in C# is to use a readonly indexer.
>
> Right. How can I acces from indexer to a private variable in a class
>
> Say, we have a class
>
> public class Foo
> {
> private ArrayList arrayList;
>
> // this property has to be an indexer as you said
> public MyIndexer readonlyproperty
> {
> get;
> }
> }
>
> Ok. Indexer would be a different class and should have an acces to
arrayList
> private variable in the class Foo. How is it possible? If we talking about
> some variable inside Indexer class itself, class Foo has to have access to
> this variable. BUT that means, I shoud give this variable higher level of
> visibility rather than private. Which VERY bad for safety.
>
> ?!?
>
> >
> > "Konstantin Kipa" <konstantin@metaobjects.net> wrote in message
> > news:3a39e24e@news.devx.com...
> > > Hi
> > >
> > > The interesting thing is, what is the standard pattern to do this? For
> > > example, I want to create read-only indexed property and do some
> > > calculations on get {} method. How can I do this?
> > >
> > > The pattern was - I had a private variable (array or collection) and
> > access
> > > this variable from my read-only indexed property.
> > >
> > > Any ideas?
> > >
> > > Thanks in advance
> > >
> > > Konstantin Kipa
> > >
> > >
> >
> >
>
>