Can someone give me a list, or point me to where I can find a list of C# data types that can be a nullable type?
For example:
I know that `Nullable<int>` is ok
I know that `Nullable<byte[]>` is not.
I'd like to know which types are nullable and which are not. BTW, I know I can test for this at runtime. However, this is for a code generator we're writing, so I don't have an actual type. I just know that a column is "string" or "int32" etc.
Thanks.
All value types (except Nullable<T> itself) can be used in nullable types – i.e. all types that derive from System.ValueType (that also includes enums!).
The reason for this is that Nullable is declared something like this:
struct Nullable<T> where T : struct, new() { … }
It can be any value type including struct, it cannot be a reference type, as those are inherently nullable already.
Yes: Int32 double DateTime CustomStruct etc.
No: string Array CustomClass etc.
For more information, see MSDN: http://msdn.microsoft.com/en-us/library/2cf62fcy(v=VS.80).aspx
A type is said to be nullable if it can be assigned a value or can be assigned null, which means the type has no value whatsoever. Consequently, a nullable type can express a value, or that no value exists. For example, a reference type such as String is nullable, whereas a value type such as Int32 is not. A value type cannot be nullable because it has enough capacity to express only the values appropriate for that type; it does not have the additional capacity required to express a value of null.
The Nullable structure supports using only a value type as a nullable type because reference types are nullable by design.
The Nullable class provides complementary support for the Nullable structure. The Nullable class supports obtaining the underlying type of a nullable type, and comparison and equality operations on pairs of nullable types whose underlying value type does not support generic comparison and equality operations.
From Help Docs http://msdn.microsoft.com/en-us/library/b3h38hb0.aspx