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TOPIC: Indexer Syntax

Indexer Syntax 9 months 2 weeks ago #6105

  orangesocks's Avatar Topic Author orangesocks Offline Posts: 32
Hi,
I'm converting some classes that I made in C# to X# as an exercise to better understand the syntax.
I'm stuck with the definition of an indexer. I looked in the documentation and I was not able to find anything.

In C# I would write:
public <TypeToReturn> this[<TypeToUse> <Value>]
{
get { <some code>; }
set { <some code>; }
}

What is the syntax to be used in X# ?

Regards Giuseppe

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Indexer Syntax 9 months 2 weeks ago #6106

  Fabrice's Avatar Fabrice Offline Posts: 52
Hi Giuseppe,
it can be something like :
PROPERTY SELF[ index AS TypeToUse ] AS TypeToReturn
GET
LOCAL item AS TypeToReturn
item := DoWhateverYouWant()
RETURN item
END GET
END PROPERTY

HTH
Fab

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Indexer Syntax 9 months 2 weeks ago #6107

  orangesocks's Avatar Topic Author orangesocks Offline Posts: 32
Hi Fab
It worked like a charm. Thanks a lot.

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Indexer Syntax 9 months 2 weeks ago #6110

  Chris's Avatar Chris Offline Posts: 1179
Guys,

One additional thing worth mentioning, is that X# supports also regular indexed (named) properties, in addition to indexers:
FUNCTION Start() AS VOID 
	LOCAL IMPLIED o := TestClass{}
	? o:IndexedProperty[123]
RETURN

CLASS TestClass
	PROPERTY IndexedProperty[n AS INT]
		GET
			RETURN n * 2
		END GET
	END PROPERTY
END CLASS

I think those are not supported in c# at all, but we had to implement them in X# (and earlier in Vulcan) because VO does support them as well (and they are often very useful).

Chris
XSharp Development Team
chris(at)xsharp.eu

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Indexer Syntax 9 months 2 weeks ago #6115

  FFF's Avatar FFF Offline Posts: 577
Chris,
out of curiosity, what's the difference to using a method - apart from braces vs. brackets ;-?

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Indexer Syntax 9 months 2 weeks ago #6117

  Chris's Avatar Chris Offline Posts: 1179
Hi Karl,

Under the hood not much, both actually are implemented like methods internally. What changes is the syntax used to access/assign the indexer from user code:
LOCAL IMPLIED o := TestClass{}
? o:IndexedProperty[123]
o:IndexedProperty[123] := 10 // if we add a SEtter to our property as well

Granted, you could recode things so that it uses a method (actually 2 methods, one for reading and one for writing), but in many cases the PROPERTY syntax is more intuitive. It's the same thing as with regular properties, what's the difference of having oWindow:Caption instead of oWindow:GetCaption() and oWindow:SetCaption(cNewCaption) ?

Chris
XSharp Development Team
chris(at)xsharp.eu

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