Cast create error while as not

Question

I have little peace of code:

private static void Casting<T>(T obj)
{
    String str = (String)obj; //Error
    str = obj as String;
}

Line String str = (String)obj returns me compile-time error

"Error CS0030 Cannot convert type 'T' to 'string'"

Lets say, I agree with the error. But why second line do not same behavior? So my question is - why "as" do not generate the error, while casting do?

What is this code supposed to be doing exactly? Not everything will convert to a string — Sayse, Jun 26 '15 at 07:30

score 2 · Answer 1 · answered Jun 26 '15 at 07:33

2

When using as, if a cast is not possible, null is returned instead of throwing an exception like a 'normal' cast would do.

See : https://msdn.microsoft.com/en-us/library/cscsdfbt.aspx

answered Jun 26 '15 at 07:33

Tom C.

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i am not talking about runtime. I am talking about compile time – zzfima Jun 26 '15 at 07:41
@zzfima - Compile time is the exact same answer, because `as` can handle it, there is no need to invent warnings/errors about something the developer probably already knows – Sayse Jun 26 '15 at 07:53

score 1 · Answer 2 · edited Jun 26 '15 at 13:28

1

By using (String)obj you say to compiler "Hey I am absolutely sure that this type can be converted to a string - just do it!" where in as operator - it's when you allow compiler to do it's job and say 'please try to convert it for me if it's possible'...

Something like this :D

edited Jun 26 '15 at 13:28

Searock

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answered Jun 26 '15 at 07:37

Fabjan

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Cast create error while as not

2 Answers2