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Compiler Error C3225

Error Message

generic type argument for 'arg' cannot be 'type', it must be a value type or handle type

The generic type argument was not of the correct type.

For more information, see Generics (Visual C++).


You cannot instantiate a generic type with a native type. The following sample generates C3225.

// C3225.cpp
// compile with: /clr
class A {};

ref class B {};

generic <class T>
ref class C {};

int main() {
   C<A>^ c = gcnew C<A>;   // C3225
   C<B^>^ c2 = gcnew C<B^>;   // OK

The following sample creates a component using C#. Notice that the constraint specifies that the generic type can only be instantiated with a value type.

// C3225_b.cs
// compile with: /target:library
// a C# program
public class MyList<T> where T: struct {}

This sample consumes the C#-authored component, and violates the constraint that MyList can only be instantiated with a value type other than Nullable. The following sample generates C3225.

// C3225_c.cpp
// compile with: /clr
#using "C3225_b.dll"
ref class A {};
value class B {};
int main() {
   MyList<A> x;   // C3225
   MyList<B> y;   // OK