Default accessor in MC++

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Daniel =?iso-8859-1?Q?Lidstr=F6m?= - 27 May 2004 10:36 GMT

I have a CS class I wish to write in MC++:

public class UnitsCollection : ArrayList
{
new public Units this[int index]
{
get { return (Units) base[index]; }
set { base[index] = value; }
}
}

Would the MC++ class below be equivalent?

[DefaultMember("Item")]
public __gc class UnitsCollection : public ArrayList
{
public:
__property Units* get_Item(int index) {
return (Units*)__super[index];
}
__property void set_Item(Units* u) {
__super::Add(u);
}
};

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Daniel

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Jesse McGrew - 28 May 2004 05:48 GMT

Daniel Lidström wrote:

> I have a CS class I wish to write in MC++:
>
[quoted text clipped - 20 lines]
> }
> };

MC++ doesn't support C#'s indexer syntax.. instead of
'collection[index]' you must write 'collection->Item[index]', and so on.
In this case you need '__super::Item[index]'. Also, since get_Item takes
an index, set_Item should also.

Try changing the property accessors as follows:

__property Units* get_Item(int index) {
return (Units*)__super::Item[index];
}
__property void set_Item(int index, Units* u) {
__super::Item[index] = u;
}

Jesse

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Daniel =?iso-8859-1?Q?Lidstr=F6m?= - 28 May 2004 08:30 GMT

> Daniel Lidström wrote:
>> I have a CS class I wish to write in MC++:
[quoted text clipped - 35 lines]
> __super::Item[index] = u;
> }

When I try this I get the following compile error:
error C2392: 'LX::Units __gc *LX::UnitsCollection::get_Item(int)' :
covariant returns types are not supported in managed types

I think it means Item is already in the baseclass. Would it be a solution
to change to

__property Units* UnitsCollection::get_Index(int index) {
return (Units*)__super::Item[index];
}
__property void UnitsCollection::set_Index(int index, Units* u) {
__super::Item[index] = u;
}

And put [System::Reflection::DefaultMemberAttribute("Index")] attribute on
the UnitsCollection class?

Is this how I use the default accessor? It compiles anyhow.

UnitsCollection* units = new UnitsCollection;
Units* unit = new Units();
units->Index[0] = unit;

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Daniel

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Jesse McGrew - 28 May 2004 19:37 GMT

Daniel Lidström wrote:

> When I try this I get the following compile error:
> error C2392: 'LX::Units __gc *LX::UnitsCollection::get_Item(int)' :
[quoted text clipped - 12 lines]
> And put [System::Reflection::DefaultMemberAttribute("Index")] attribute on
> the UnitsCollection class?

Yes.

The compiler thinks you're trying to override ArrayList's get_Item
method (which is virtual) instead of replacing it, since yours has the
same parameters, but the return type differs so you get an error. In C#,
you could use the 'new' keyword to hide the inherited member instead of
overriding it, but I don't think MC++ has an equivalent.

> Is this how I use the default accessor? It compiles anyhow.
>
> UnitsCollection* units = new UnitsCollection;
> Units* unit = new Units();
> units->Index[0] = unit;

Yes.

In MC++ the default accessor is no different from any other indexed
property. The [DefaultMember] attribute only affects other languages
such as C#.

Jesse

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Default accessor in MC++

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