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.NET Forum / Languages / C# / January 2008newbie question: how to test whether a variable is a value type
for reference type, I can use the is keyword, but how can test whether a specific type is a value type? Sorry for the stupid question, the answer is is ValueType Hi, Type.IsValueType Which is myinstance.GetType().IsValueType > for reference type, I can use the is keyword, but how can test > whether a specific type is a value type?  SignatureIgnacio Machin http://www.laceupsolutions.com Mobile & warehouse Solutions. There is a problem with this (and the OP's solution) when it comes to nullable types. Assuming the value is in an object (if it was typed, then there would be no reason to check for it in the first place, since you can always do "typeof(KnownType).IsValueType"), and the value from a Nullable<T> which was null was stored to it, you would end up with an object reference of null, with no way of calling GetType. When boxing the nullable value, it actually puts null (not a Nullable<T> with a value of null) in the object reference. There really is no good way of doing this if you are using Nullable values along with an object reference and want to call GetType on that variable. Signature- Nicholas Paldino [.NET/C# MVP] - mvp@spam.guard.caspershouse.com > Hi, > [quoted text clipped - 5 lines] >> for reference type, I can use the is keyword, but how can test >> whether a specific type is a value type? > There really is no good way of doing this if you are using Nullable > values along with an object reference and want to call GetType on that > variable. Absolutely true - but generics (with type inference) can help a little bit - i.e. if you have SomeMethod<T>(T whatever) then the caller can use SomeMethod(localTypedValue), and then if needed you can use typeof(T).IsValueType (or whatever). Again, however, you are completely scuppered if you get down to "object"... I guess the point I'm trying to make is that: in addition to "object" as a parameter, generics *also* provide a mechanism for writing a utility method dealing with an unpredictable object-type (normally without changing the call syntax). However, to be effective (i.e. typeof(T) to be useful), the calling method *must* know the actual type [even if just another "T"] (not just "System.Object"). Marc Marc, I thought of that, but omitted it because if the type was known at compile time, the whole conversation is moot, but it is a valid point (assuming you know the type at compile time). Signature- Nicholas Paldino [.NET/C# MVP] - mvp@spam.guard.caspershouse.com >> There really is no good way of doing this if you are using Nullable >> values along with an object reference and want to call GetType on that [quoted text clipped - 13 lines] > > Marc Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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