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User-Defined Operators

User-defined operators for managed types are allowed as static or instance members of managed types, or at global scope. However, only static operators will be accessible via metadata to clients written in a language other than Visual C++.

When a static user-defined operator is in a reference type, one of the parameters of the user-defined operator must be either:

  • A handle (type ^) to an instance of the enclosing type,

  • A reference type indirection (type^& or type^%) to a handle to an instance of the enclosing type.

When a static user-defined operator is in a value type, one of the parameters of the user-defined operator must be either:

  • Of the same type as the enclosing value type.

  • A pointer type indirection (type^) to the enclosing type.

  • A reference type indirection (type% or type&) to the enclosing type.

  • A reference type indirection (type^% or type^&) to the handle.

  • You can define the following operators:

Operator Unary/Binary Forms?

!

Unary

!=

Binary

%

Binary

&

Unary and Binary

&&

Binary

*

Unary and Binary

+

Unary and Binary

++

Unary

,

Binary

-

Unary and Binary

--

Unary

->

Unary

/

Binary

<

Binary

<<

Binary

<=

Binary

=

Binary

==

Binary

>

Binary

>=

Binary

>>

Binary

^

Binary

false

Unary

true

Unary

|

Binary

||

Binary

~

Unary

// mcppv2_user-defined_operators.cpp
// compile with: /clr
using namespace System;
public ref struct X {
   X(int i) : m_i(i) {}
   X() {}

   int m_i;

   // static, binary, user-defined operator
   static X ^ operator + (X^ me, int i) {
      return (gcnew X(me -> m_i + i));
   }

   // instance, binary, user-defined operator
   X^ operator -( int i ) {
      return gcnew X(this->m_i - i);
   }

   // instance, unary, user-defined pre increment operator
   X^ operator ++() {
      return gcnew X(this->m_i++);
   }

   // instance, unary, user-defined post increment operator
   X^ operator ++(int i) {
      return gcnew X(this->m_i++);
   }

   // static, unary user-defined pre and post increment operator
   static X^ operator-- (X^ me) {
      return (gcnew X(me -> m_i - 1));
   }
};

int main() {
   X ^hX = gcnew X(-5);
   System::Console::WriteLine(hX -> m_i);

   hX = hX + 1;
   System::Console::WriteLine(hX -> m_i);

   hX = hX - (-1);
   System::Console::WriteLine(hX -> m_i);

   ++hX;
   System::Console::WriteLine(hX -> m_i);

   hX++;
   System::Console::WriteLine(hX -> m_i);

   hX--;
   System::Console::WriteLine(hX -> m_i);

   --hX;
   System::Console::WriteLine(hX -> m_i);
}

Output

-5
-4
-3
-2
-1
-2
-3

This sample demonstrates operator synthesis, which is is only available when compiling with /clr. Operator synthesis creates the assignment form of a binary operator if one is not defined, and where the left-hand side of the assignment operator has a CLR type.

// mcppv2_user-defined_operators_2.cpp
// compile with: /clr
ref struct A {
   A(int n) : m_n(n) {};
   static A^ operator + (A^ r1, A^ r2) {
      return gcnew A( r1->m_n + r2->m_n);
   };
   int m_n;
};

int main() {
   A^ a1 = gcnew A(10);
   A^ a2 = gcnew A(20);

   a1 += a2;   // a1 = a1 + a2   += not defined in source
   System::Console::WriteLine(a1->m_n);
}

Output

30

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