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Compiler Error C3216

  • Article

constraint must be a generic parameter, not 'type'

A constraint was ill formed.

The following sample generates C3216:

// C3216.cpp
// compile with: /clr
interface struct A {};

generic <class T>
where F : A   // C3216
// Try the following line instead:
// where T : A    // C3216
ref class C {};

The following example demonstrates a possible resolution:

// C3216b.cpp
// compile with: /clr /c
interface struct A {};

generic <class T>
where T : A
ref class C {};