Compiler Error C3391
Visual Studio 2015
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The latest version of this topic can be found at Compiler Error C3391.
type_arg' : invalid type argument for generic parameter 'param' of generic 'generic_type', must be a non-nullable value type
A generic type was instantiated incorrectly. Check the type definition. For more information, see Nullable and Generics.
The following sample, using C#, creates a component that contains a generic type, with certain constraints that are not supported when authoring generic types in Visual C++ 2005. For more information, see .Constraints on Type Parameters.
// C3391.cs
// compile with: /target:library
// a C# program
public class GR<N>
where N : struct {}
The following sample generates C3391.
// C3391_b.cpp
// compile with: /clr
#using <C3391.dll>
using namespace System;
value class VClass {};
int main() {
GR< Nullable<VClass> >^ a =
gcnew GR< Nullable<VClass> >(); // C3391 can't be Nullable
GR<VClass>^ aa = gcnew GR<VClass>(); // OK
}
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