Object/Decimal cast exception... Bug ? or is it me ?

[TheSteph]

Why do I get an exception "The specified cast is not valid" ??? Is that a
bug or do I miss something ?


object DecimalObject = 1;
decimal TmpDecimal;
TmpDecimal = (decimal)DecimalObject;



Steph.

 

[Stoitcho Goutsev \(100\)]

It is not a bug.
You can unbox value type only to the exact type of the object.

They way you box the value you don't get decimal boxed object

the following code works:

object DecimalObject = 1m;
decimal TmpDecimal;
TmpDecimal = (decimal)DecimalObject;

Note the 'm' sufix after the 1 that instructs the compiler that the litteral
constant is a decimal number.

 

[Nicholas Paldino [.NET/C# MVP]]

You could also do this:

object DecimalObject = 1;
decimal TmpDecimal = (decimal)(int) DecimalObject;

Not clean, but it is possible.

If you have a boxed instance, it is better to use the Convert class
instead, so that you can avoid having to "know" what is in the boxed
instance.

Hope this helps.

 

[TheSteph]

Thanks !!!

In fact I didn't know that : "You can unbox value type only to the exact
type of the object".... so the bug was in my brain ;-)

Steph.

 

[Jon Skeet [C# MVP]]

It is not a bug.
You can unbox value type only to the exact type of the object.

There's one exception to this: enums. You can unbox a boxed enum value
to the underlying type of the enum, or to any other enum with the same
underlying type. Similarly you can unbox a boxed value of an integer
type to any enum with that type as the underlying type.

Oh, and the C# and CLI specs currently don't spell this out properly.

See, I knew that tidbit of useless information would come in handy one
day