Setting the variable as type

Question

Found this piece of code today:

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

Why as EventFeed at the end? The return type of this function is already EventFeed , so I try my best to see the advantage of such a statement.

It was hard for me to find this problem, so I ask here. What are the benefits of writing such a line?

Answer 1

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

Using as stops an exception from the created exception and as a result it turns out null if the result of the expression cannot be distinguished as EventFeed .

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

Answer 2

It depends on the DataType returned by the Query call. as in this case will try to pass the result to the EventFeed type, otherwise return null .

Answer 3

object may be returned in your request

 service.Query(eventQuery) 

so that you select this object as your data type.

Answer 4

If the method signature for Query indicates that it returns an EventFeed (as opposed to returning a base class, but you KNOW its EventFeed ). then as not required.

Just because you declare feed as an EventFeed does not mean that the object you are returning from Query is. You might be trying to fit a square pin into a round hole.

Answer 5

According to your changes, if service.Query already returns "EventFeed", processing it as such does nothing. Looks like duplicate code.