C#2.0 Dictionary<Key, Value> indexer operation is strange?

[I am dog]

Hi ,

I use VS 2005 beta1 to do some thing as follows.

declare a Dictionary<ulon g,DelegateTyep> dictionary = new ...

and use dictionary object such as

dictionary [aUlongNumber] += aDelegateTyepOb ject;

then compiler is ok ,but throw KeyNotFoundExce ption at run-time.
OK,I think just a missed initailization, thne add it like

dictionary[aUlongNumber] = null;

It becomes to be vary strange.It doesn't throw exception any more.

What's difference between '=' and '+=' on Dictionary's indexer operation?
Them are also assigning value to indexing entry,right?
Or some thiing compiler do for '+=' operator(Delega te.Combine)?

Thanks for your help

[Mattias Sjögren]

What's difference between '=' and '+=' on Dictionary's indexer operation?

The same as always; += expands to

dictionary[aUlongNumber] = dictionary[aUlongNumber] +
aDelegateTypeOb ject;

and retrieving dictionary[aUlongNumber] before you have added that key
to the dictionary will throw an exception.

Mattias

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Mattias Sjögren [MVP] mattias @ mvps.org
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