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.NET Forum / Languages / C# / February 2008Confused with properties declaration
Hi, I mainly develop in C++ and Java but I think I have a basic understanding of C# which I use occasionally only. I came across the following declaration of properties in on line docs: DbParameterCollection.Item(Int32) DbParameterCollection.Item(String) Since this is not a 'typical' declaration of properties (e.g. not <accessmod><return><name> + accessors) I don't really know how to interpret it. How do I access items? Assuming that the collection is 'params', 'name' is a valid string, and 'i' is a valid index,can I simply do the following? params.Item[index] = param; param = params.Item[index]; params.Item[name] = param; Could someone please provide me with a quick explanation? Any pointers to on-line docs will also be very helpful. Thanks, Bogdan Bogdan, It would be helpful if you show the link where you saw the declaration, as it would help provide context. What you want to look at is "indexers": http://msdn2.microsoft.com/en-us/library/6x16t2tx.aspx As there is no need to call the Item property directly in C#.  Signature- Nicholas Paldino [.NET/C# MVP] - mvp@spam.guard.caspershouse.com > Hi, > [quoted text clipped - 18 lines] > Thanks, > Bogdan Thanks for the reply. I was initially thinking of indexers but I had doubts because of the fact that there were no square brackets in the declaration and docs clearly stated that they were properties. The link that I was referring to is at: http://msdn2.microsoft.com/en-us/library/system.data.common.dbparametercollectio n.item.aspx So, how shoud I interpret the following syntax: Item(Int32)? Is this an indexer that can be accessed by an integer index? If yes, do C# specs have this syntax defined somewhere? Thanks, Bogdan > Bogdan, > [quoted text clipped - 29 lines] >> Thanks, >> Bogdan > Thanks for the reply. I was initially thinking of indexers but I had doubts > because of the fact that there were no square brackets in the declaration [quoted text clipped - 47 lines] > > - Show quoted text - Make sure you are looking at the C# example and not the VB example. Under the hood, C# convert all properties to methods: <value_type> get_PropertyName void set_PropertyName(<value_type> value) When working with Indexers, those methods look like this: <value_type> get_Item(<list of indices>); void set_Item(<list of indices>, <value_type> value); Some times when looking at a property either through a COM Interop or through VB you will just see Item. Here you just pass the indices as arguments. It is just like saying: myClass[<list of indices>] In C++, overloading the [] operator is no different, except .NET converts it to a method call under the hood. Am I answering your question? [...] >Make sure you are looking at the C# example and not the VB example. >Under the hood, C# convert all properties to methods: [quoted text clipped - 17 lines] > >Am I answering your question? Yes. Thanks. The COM Interop was a good clue. Bogdan, Well, an indexer is usually just shorthand for an indexed property. You could call it directly if you wanted, but I don't see the point. The syntax means that if you were going to access it directly by its property, then the property you would access is the Item property. The Int32 means that you can index it on an integer (although other collections might be indexed on other things, in which case, that type will be where Int32 is). You could look in the C# programmers guide as well as the C# language specification if you are looking for the specific definition of an indexer. A google search will turn up both easily. Signature- Nicholas Paldino [.NET/C# MVP] - mvp@spam.guard.caspershouse.com > Thanks for the reply. I was initially thinking of indexers but I had > doubts because of the fact that there were no square brackets in the [quoted text clipped - 42 lines] >>> Thanks, >>> Bogdan Thanks again for the reply and your patience. I get it know. I was confusing C#'s indexers and properties with .NET properties. I wrongly assummed that having language filter set to C# will cause all declarations to appear in C#. So when I saw "DbParameterCollection.Item Property" I thought that it referred to C# property of a class. > Bogdan, > [quoted text clipped - 10 lines] > specification if you are looking for the specific definition of an > indexer. A google search will turn up both easily. [...] Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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