CODEWITHSUNDEEP
c#
Mike Baxter
Mike Baxter

Reputation: 7258

Setting variable 'as type'

Came across this snippet of code today:

EventFeed feed = null;
feed = service.Query(eventQuery) as EventFeed;

Why the as EventFeed at the end? The return type of that function is already an EventFeed, so I'm struggling to see the benefit of such a statement.

I found it difficult to search for this problem so I'm asking on here. What are the advantages to writing a line like this?

Upvotes: 4

Views: 122

Answers (5)

The other other Alan
The other other Alan

Reputation: 1908

According your edit, if service.Query already returns an 'EventFeed', recasting it as such does nothing. Looks like duplicate code.

Upvotes: 0

D Stanley
D Stanley

Reputation: 152511

If the method signature for Query specifies that it returns an EventFeed (as opposed to returning a base class but you KNOW it's an EventFeed). then the as is unnecessary.

Just because you declare feed as an EventFeed doesn't mean that the object you get back from Query is. You may be trying to put a square peg in a round hole.

Upvotes: 0

Dave Bish
Dave Bish

Reputation: 19646

It depends on the DataType returned from the Query call. as in this case will attempt to cast the result to the EventFeed type, otherwise return null.

Upvotes: 1

Sachin
Sachin

Reputation: 40970

Your query may be returning an object

service.Query(eventQuery)

so you are casting this object as your data type.

Upvotes: 1

Lloyd
Lloyd

Reputation: 29668

feed might be declared as EventFeed however the result of service.Query(eventQuery) may not be.

Using as stops an exception from being thrown and you end up with null instead if the result of the expression cannot be cast as EventFeed.

You can read more about as here - http://msdn.microsoft.com/en-us/library/cscsdfbt(v=vs.71).aspx

Upvotes: 7

Related Questions