Compiler Error C3390

 

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The latest version of this topic can be found at Compiler Error C3390.

type_arg' : invalid type argument for generic parameter 'param' of generic 'generic_type', must be a reference type

A generic type was instantiated incorrectly. Check the type definition. For more information, see 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.

// C3390.cs  
// compile with: /target:library  
// a C# program  
public class GR<C, V, N>  
where C : class  
where V : struct  
where N : new() {}  

The following sample generates C3390.

// C3390_b.cpp  
// compile with: /clr  
#using <C3390.dll>  
ref class R { R(int) {} };  
value class V {};  
ref struct N { N() {} };  
  
int main () {  
   GR<V, V, N^>^ gr2;   // C3390 first type must be a ref type  
   GR<R^, V, N^>^ gr2b;   // OK  
}  

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