casting from object

[Tony Johansson]

Hello!

Can somebody tell me why this
Object o = 1;
long d = (long)o;

doesn't work.
Here I know that the value 1 is copied and created on the heap and
the reference o which exist on the stack is refering to the created memory
on the heap.
I know that this will throw invalidcastExce ption and the cast must have
exactly the same type
in this case int.
But I mean that assigning an int to a long would'n be too bad so
the run time could exept it.

I mean this works fine assigning an int to long
int i = 1;
long l = i;

//Tony

[Jon Skeet [C# MVP]]

Re: casting from object

Tony Johansson <johansson.ande rsson@telia.com wrote:

Can somebody tell me why this
Object o = 1;
long d = (long)o;
>
doesn't work.
Here I know that the value 1 is copied and created on the heap and
the reference o which exist on the stack is refering to the created memory
on the heap.
I know that this will throw invalidcastExce ption and the cast must have
exactly the same type
in this case int.
But I mean that assigning an int to a long would'n be too bad so
the run time could exept it.

Unboxing has to be precise - the cast above is an unboxing cast instead
of a conversion cast.

You can change the code to this, however, which will work:

object o = 1;
long d = (int) o;

I mean this works fine assigning an int to long
int i = 1;
long l = i;

And that implicit conversion is why my code above will work.

--
Jon Skeet - <skeet@pobox.co m>
Web site: http://www.pobox.com/~skeet
Blog: http://www.msmvps.com/jon.skeet
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