The following rules apply to unary operator declarations, where T denotes the class or struct type that contains the operator declaration:

• A unary +, -, !, or ~ operator must take a single parameter of type T and can return any type.
• A unary ++ or --operator must take a single parameter of type T and must return type T.
• A unary true or false operator must take a single parameter of type T and must return type bool .

The signature of a unary operator consists of the operator token (+, -, !, ~, ++, --, true, or false) and the type of the single formal parameter. The return type is not part of a unary operator's signature, nor is the name of the formal parameter.

The true and false unary operators require pair-wise declaration. A compile-time error occurs if a class declares one of these operators without also declaring the other. The true and false operators are described further in 14.16.

[Example: The following example shows an implementation and subsequent usage of operator++ for an integer vector class:

public class IntVector { public int Length { ... } // read-only property public int this[int index] { ... } // read-write indexer public IntVector(int vectorLength) { ... } public static IntVector operator++(IntVector iv) { IntVector temp = new IntVector(iv.Length); for (int i = 0; i < iv.Length; ++i) temp[i] = iv[i] + 1; return temp; } } class Test { static void Main() { IntVector iv1 = new IntVector(4); // vector of 4x0 IntVector iv2; iv2 = iv1++; // iv2 contains 4x0, iv1 contains 4x1 iv2 = ++iv1; // iv2 contains 4x2, iv1 contains 4x2 }

Note how the operator method returns the value produced by adding 1 to the operand, just like the postfix increment and decrement operators(14.5.9), and the prefix increment and decrement operators (14.6.5).

Unlike in C++, this method need not, and, in fact, must not, modify the value of its operand directly. end example]